Dad the Veteran: Glóin was a veteran of both the Battle of Azanulbizar and the Battle of the Five Armies before fathering Gimli, one of the heroes of the War of the Ring.
Darkest Hour: Happens at least once in each book; Frodo's flight to Rivendell pursued by all nine of the Nazgûl, the Bridge of Khazad-dûm, the Breaking of the Fellowship, the Battle at Helm's Deep, The orcs finding Frodo at Shelob's lair, the Siege of Gondor, the Battle at the Black Gates.
The best example of all is in Sammath Naur. At the brink of triumph, Frodo claims the Ring for himself, almost dooming the quest and all Middle-Earth, and Sauron discovers he is there. Conversely, this is also the Darkest hour for Sauron in all his existence. The Ring is in the only place in the Earth in which it can be destroyed, he discovers how deeply he has been deceived, and he knows his destiny is hanging on by a thread, because he knows that if the Ring falls into the fire, he is finished for good, so the Nazgûl come back running at all speed.
Dark Is Evil: Different nations and peoples on both ends of the good-evil-spectrum have used black as their colour, or have black hair. It seems that Sauron likes this trope, as Éomer mentions in The Two Towers that agents of Sauron routinely steal black horses, to the point where there are practically none left in Rohan.
Darker and Edgier: The former though not necessarily the latter. Compared to The Hobbit, the stakes are much higher and the perils the protagonists face more sinister. However it'd still be hard to describe as "edgy," in fact it's usually praised for still being an overall wholesome work despite the overall darker tone.
The Darkness Before Death: While Théoden lies dying on the Pelennor, he tells Merry not to grieve his passing and to send for Éomer because his eyes darken, and he wants to see him before he passes.
David vs. Goliath: While Sauron's troops are individually inferior to those of the Free Peoples, he has so many of them (plus his own powerful magic) that The Alliance has no chance at a purely conventional victory, a point emphasized repeatedly.
Dawn Attack: The Rohirrim like to do this when they're playing The Cavalry. Both Erkenbrand's charge to break the siege on Helm's Deep and Théoden's attack at the Battle of Pelennor Fields happen at dawn.
Dead Guy Junior: Or at least Departed Guy Junior. Sam names his eldest son Frodo, and a later son Bilbo. It's not known whether either of those characters is still alive at the time. Incidentally, he also names two sons after Merry and Pippin.
Subverted in The Two Towers. The lines quoted below sound like they are going to be this trope, but both characters survive and the conversation presumably happens at some point. Faramir to Frodo:
"I would gladly learn how this creeping Smeagol became possessed of the Thing of which we speak, and how he lost it, but I will not trouble you now. If ever beyond hope you return to the lands of the living and we re-tell our tales, sitting by a wall in the sun, laughing at old grief, you shall tell me then."
Played straight in the same book. Théoden doesn't have time to sit and chat about Merry's ancestors and pipe-weed when they meet at Isengard, but promises that they will have as long a conversation as the hobbits could ask for once they're all sat in peace at Meduseld. However, the events of the War sweep them away and Theoden dies without ever having the opportunity to make good on his word.
The Mouth of Sauron: I am an ambassador and may not be assailed!
Death Seeker: Éowyn feels that she's been rejected by Aragorn and that she's no longer needed by Theoden
"He caught the glint of clear grey eyes; and then he shivered, for it came suddenly to him that it was the face of one without hope who goes in search of death."
Deconstruction: Of the more conventional heroic fantasy in which The Hero gains power to overthrow evil and achieve happiness. In Tolkien's story, anyone strong enough to use the One Ring to defeat Sauron would themselves become, in the process, as evil as Sauron (or worsenote In one of his letters, Tolkien stated that Gandalf claiming the Ring would lead to a worse situation than Sauron recovering it, because at least Sauron was openly evil, whereas Gandalf with the Ring would do evil in the name of good, thereby corrupting even the idea of good). The main protagonist is a Classical Anti-Hero who is The Only One for the job for this very reason, and his mission is to throw away the only weapon powerful enough to defeat their Enemy (several characters comment on the seeming folly of this). Moreover, at the end of the story, Frodo, rather than finding happiness, suffers from physical and spiritual wounds that will not heal, and must eventually leave Middle-Earth altogether.
Although deconstruction wouldn't be around in name until a decade and a half after The Lord of the Rings was published (and then only in French), Tolkien's letters clearly show that he did intend his book to interrogate conventional ideas about heroism. Frodo Baggins's fate in particular was inspired by Tolkien's own experiences in the First World War.
Demonic Possession: Merry seems to be possessed by - or at least sharing a memory with - one of the wights when he and the other hobbits are trapped in the barrow, as he says that one of the "men of Carn Dum" had mortally wounded him. He snaps out of it after a moment.
Dénouement: "The Grey Havens" takes place after the death of every villain and details what exactly the world has lost in the process of destroying the One Ring.
Despair Event Horizon: Denethor during the Siege of Gondor, which leads to him trying to immolate himself and his son on a funeral pyre.
Despair Gambit: Sauron runs several of these, one culminating in the point immediately above. His armies also make use of it in their tactics, and the Nazgûl have it in a supernatural, weaponized form, which gets more powerful in places of terror, despair and loneliness.
Despair Speech: Denethor gives several speeches, each more long-winded than the last, about how Gondor is doomed against the might of Mordor.
Deus ex Machina: Eagles repeatedly show up when absolutely nobody else can get the heroes out of a situation... but never appear any other time they might be just a bit useful. Possibly a more literal situation than many, since they may have ties to the Valar.
Tolkien himself said in a letter than he realized they were a Deus Ex Machina, hence why he didn't like using them often because they make solving problems too easy. He also mentioned that the Eagles themselves are aware of being an easy Deus Ex Machina and would never stoop to being Middle-earth's taxi service.
Aragorn, Gimli and Legolas cover an incredible distance on foot with little food or rest while chasing Saruman's orcs.
Gollum, Frodo and Sam, especially when going through Mordor. They have to cross a parched desert plateau on foot with practically no provisions.
Did You Just Flip Off Cthulhu?: The Gaffer, Sam's elderly father and Bilbo's gardener, tells Khamûl, second-in-command of the Nazgûl, to get lost when he comes calling to Bag End just after Frodo leaves. Of course, he doesn't know who this is (or that the Nazgul have strict no-murder-spree-til-you-find-the-Ring orders), but it's still a hundred-year-old, three-foot-tall man telling a dark and terrible armed horseman that "Mister Frodo's" whereabouts are none of his damn business.
Éowyn and Merry, two mortal civilians who snuck into the army, destroy the Lord of the Nazgûl, a group of nine undead sorcerers.
Sam mutilates Shelob, an ancient being that doesn't answer to Sauron.
Somewhat downplayed in the narration making clear, that neither Sam nor some of the greatest heroes of Men (Turin and Beren are specifically namedropped) would have the power to hurt her so. Shelob herself lowering her bulk on a blade pointing upwards though... At the very least we know that she was badly injured and hors de combat for a long time.
Gandalf: That we should wish to throw him down and have no one in his place is not a thought that occurs to him.
Diplomatic Impunity: The Mouth of Sauron invokes this when it looks as if Aragorn is about to cut him up into little pieces. Perhaps surprisingly Aragorn allows it to fly, only commenting that where such laws hold diplomats are usually less insolent. It probably didn't help the Mouth too much in the long run though.
Direct Line to the Author: The core of the story (The Hobbit and The Lord of the Rings) exist In-Universe as Bilbo's diary and Frodo's account of his adventures, and is called the Red Book of Westmarch. This original Red Book was copied into an edition called The Thain's Book, to which someone added a few volumes of "Translations from the Elvish" by Bilbo. This was copied in turn by one "Findegil, the King's Writer" — the date this copy was made is the last dated event in the book, so we can presume Tolkien "discovered and translated" this copy. The story begins with Bilbo's homely descriptions of the hobbit characters' interaction, gradually changes to Frodo's scholarly and slightly purple narration throughout most of the rest of the book, and ending with Sam's down-to-earth, humble (but still educated) language towards the end — the second half of Book Six, detailing the Scouring and renewal of the Shire, is directly implied to have been written by Sam ("I have finished. The last few pages are for you").
Dirty Business: When Frodo lures Gollum into the hands of Faramir's men. Gollum never forgives him even though it was for his own good, and it seems to have cemented his plans for treachery. He acts much more like Gollum and less like Sméagol afterwards.
Disney Death: Happens to Frodo twice, first when he is stabbed by an Orc and second when he is stung by Shelob. His mithril armour saved him the first time, and Shelob used paralytic poison instead of a fatal one so she could eat him alive later.
Distant Finale: There is an epilogue with Sam and his children after having just finished a reading of the book. Tolkien decided against including it in the original books, but it was eventually published in The History of Middle-earth 9: Sauron Defeated.
Distant Sequel: The Lord of the Rings begins sixty years after The Hobbit, and the main bulk of the action another seventeen years after that; this is not immediately noticeable due to most main characters belonging to species that are either very Long-Lived or actually ageless, but enough time has passed for Bilbo to become an old man with an adult nephew and for the city of Dale to be ruled by the grandson of Bard, who becomes its ruler at the end of The Hobbit.
Distinguished Gentleman's Pipe: In the books, pretty much everyone smokes a pipe. But the older, more established authority figures are seen smoking them more often.
Divided for Publication: Tolkien hated the idea of splitting it up, but the publisher insisted on publishing the novel in three separate volumes, due to a long-running postwar paper shortage. This is the root of the mistaken belief of the Lord of the Rings as a trilogy, and ironically might have inspired the trend for fantasy to be written in trilogies.
Divine Birds: The eagles serve as the emissaries of the Valar, providing Divine Intervention at several critical moments. By contrast, in The Hobbit they were more independent and only helped the protagonists at their own convenience.
Doctor's Orders: Faramir is reluctant to override the Warden of the Houses of Healing when Éowyn asks.
Doomed Hometown: The Shire, though it's sort of inverted. You Can Go Home Again, but home is not the same: the Big Bad is defeated, but the homeland they set out to protect has become a Dystopia. There aren't even any hints of this (except a brief glimpse via Galadriel's mirror, by Sam, and even then it's not clear whether it's really going to happen—Galadriel warns of a possible Self-Fulfilling Prophecy if Sam tries to go back and stop it) until the main plot of the book is over.
Don't Think, Feel: Subverted because, after he hears that Frodo is still alive, Sam gives this admonition to himself:
You fool, he isn't dead, and your heart knew it. Don't trust your head, Samwise, it is not the best part of you. The trouble with you is that you never really had any hope.
Doomed Predecessor: Aragorn, Gimli and Legolas find the corpse of a Lord of Rohan who previously attempted to brave the Paths of the Dead, who died horribly trying to find the way out again. Aragorn identifies him as somebody who was trying to fulfill an ill-advised quest.
Doorstopper: Despite being called a trilogy, it's really just one giant book. Which the publisher divided into three volumes. Different reasons have been given: to reduce its intimidating size, to earn three sets of attention-getting reviews, or to get around the initial financial and paper-supply shortages by printing three Fellowships rather than one three-in-one. Many later editions restore the three parts to one big book, though.
Double Agent : According to Unfinished Tales one of Bill Ferny's companions ('the squint-eyed southerner') was a spy for Saruman until the Witch-King intimidated him into working for Sauron. In the book Aragorn is shown wondering who he had been working for.
Dragon Hoard: Éowyn mentions that her ancestor Fram killed "Scatha the Worm" and thus won a hoard which the dragon had robbed from dwarves.
Drama-Preserving Handicap: The Istari (Gandalf and co.) were explicitly told not to match themselves 'power for power' against Sauron. Their job was to inspire and enable the Free Peoples and thus they had to limit a lot of their own natural power. Justified in that the last time Powers of good and evil squared off directly, the world got slightly broken.
The Dreaded: Lots of examples. The Nazgûl terrify by their nature, Sauron and the Balrog command awe and fear by reputation, and the ghosts Aragorn leads into battle terrify orcs enough that they are routed before they even know if their weapons will work.
Driven to Suicide: Denethor attempts to burn himself alive in despair thanks to the lies Sauron worked into his head via the Minas Tirith Palantír.
Drums of War: After Pippin knocks a stone down the well in the Mines of Moria, the Fellowship hears drum-beats echoing up out of the well. It's not explicitly stated, but this is the sound of the orcs that now infest the mines gathering to attack the Fellowship.
In the appendices, Tolkien recounts the War of the Dwarves and Orcs, which broke out after orcs killed Thrór, heir of Durin and desecrated his body. After the final battle at the gates of Moria, there were too many dead dwarves for them to all be entombed as was the dwarven custom, so they burned them instead. A dwarf can say of his ancestor "he was a burned dwarf" and all dwarves present will know exactly what battle the ancestor died in.
Dying for Symbolism: Gandalf's sacrifice to save the party marks the nadir of the heroes' morale, his death symbolises the progress of evil forces in Middle Earth, and his resurrection and color upgrade (from Gandalf the Grey to Gandalf the White) announces the necessity, at the end of the opus, for the hero to go meet death at the Grey Heavens.
Dying Race: The Ents have lost all the Entwives, rendering them incapable of reproducing. And the Elves are slowly departing from Middle-Earth, though this is mostly because they are leaving to go to Valinor rather than dying.
Earn Your Happy Ending: Frodo and his companions - without any of the powerful help they had in the earlier parts of the book - motivate and lead the people of the Shire to restore their land's freedom and happiness.
Easing into the Adventure: The beginnings in the Shire detail parties, dinners, and celebrations before the hobbits go to war.
Eastward Endeavor: The Fellowship of the Ring travels east and south with the goal of destroying the One Ring. The destination is much more sinister than the usual setting for this trope, but it still manages to unlock the hero in Frodo and Samwise. The other Fellowship members also become incredible badasses during the quest, or even better if they already were.
The tentacled thing that trapped the Fellowship in Moria, the Watcher in the Water, is an unexplained abomination - unless it is, perhaps, one of the "nameless things" Gandalf encountered before death.
The "nameless things" that gnaw the earth, which Gandalf and the Balrog encounter far beneath Moria, are implied to be this as well. They are supposed to be so scary that Gandalf, who didn't flinch in front of the Balrog or the Witch-King of Angmar, was too horrified to even describe them. They were supposedly intended as a subtle Shout-Out to H. P. Lovecraft's works. Tolkien's earliest writing suggests they were entities with entirely separate origin from the Ainur, and perhaps even from Eru himself, but this idea was dropped as part of aligning Middle-Earth with Tolkien's own Catholic values.
It's implied that Sauron's resurgence has awoken a number of eldritch things that were asleep. The Barrow-wights may no longer be allied with Sauron, but Tolkien's copious notes indicate that they were probably roused by the presence of the Black Riders scouting out the edges of the Shire.
The thing named Ungoliant, mentioned in the text only as Shelob's mother, is another being of unknown origin and terrible intentions.
Shelob herself, to a lesser extent, being an evil spirit that takes the form of a spider.
Type "Oldest and Fatherless: The Terrible Secret of Tom Bombadil" into Google and you'll read a very plausible and disturbing theory as to what Tom Bombadil might actually be. See Eldritch Location below.
Tom Bombadill's wood qualifies, as it's impossible to navigate safely without his help, and has old and evil living tree spirits similar to the ones in Fangorn.
If we're talking just 'eldritch' and not 'spooky, filled with death and decay' as well, then Lothlórien and Rivendell would qualify due to the use of the Elven Rings to alter the perception and flow of time. Keeping track of time there becomes a complete Mind Screw for anyone who isn't an Elf.
Morgul Vale is a grotesque parody of what it was before it fell to the Nazgûl, now full of unnatural light, cold mist and mutant white flowers, and decorated with creepy statues.
Emerging from the Shadows: A revived Gandalf the White keeps his face and new garments hidden until it is time to reveal himself.
Emotion Bomb: Evil things, especially the Nazgûl, inflict terror by their very presence. In fact, fear is the Nazgûls' primary weapon.
End of an Age: The story is set at the end of the Third Age, before either Sauron rules over all or Men take the place of elves, dwarves, and Ents in Middle-earth.
Enemy Civil War: The various factions of orcs. Apparently orcs constantly killing each other when there's nothing else to fight is a side effect of Sauron filling them with rage.
Enemy to All Living Things: The Nazgûl; their horses have to be specially bred and trained just to stand being near them, let alone serving as their mounts.
Engagement Challenge: Elrond gives this to Aragorn in the backstory. If he wants Arwen's hand in marriage, he's got to earn the throne of Gondor and Arnor first. After all, who wouldn't want the best possible, comfortable and safe life for their daughter? Especially since by choosing to marry Aragorn she gives up a seat on the ships to the West and her immortality.
Even Evil Has Standards: Orcs serve Sauron, slaughter each other and non-orcs in endless racist wars, eat human flesh, and torture prisoners for fun. But they do not put up with orcs who eat orc-flesh.
The heroes' only hope hinges on the fact that Sauron can't even conceive of someone even wanting to destroy the Ring and give up that kind of power, let alone actually setting out to try. He just could not conceive that the creature holding the Ring would not chose to be a world conqueror (See Evil Is Petty). He easily fell for Aragorn's bluff of using the Ring against him, but it never occurred to him that the real intention was to take it to Mount Doom and melt it.
It's a running theme in the books. Theoden offers forgiveness to Grima Wormtongue, and the latter is baffled and thinks it's a ruse, and flees. Saruman cannot comprehend the mercy shown by the Shire when he's expelled (and it gets him killed by Grima who has had enough of Saruman's orders.)
The eye of Sauron is described as being quite fiery. Furthermore, Sauron's hand is burning hot (It's implied that he killed Gil-galad just by touching him), which is why the Ring glows on his hand and remained red-hot when first taken from him.
The Balrogs are evil spirits of fire, burning flames cloaked in shadow and armed with flaming weapons.
Inverted with the Nazgul, who can be seriously damaged (though not permanently destroyed) by ordinary men - or hobbits - armed with torches.
The Ring tempts its bearer with power fitted to their stature, and after it betrays Isildur, it ends up only in the hands of Hobbits and their river-folk kin, whose powers and ambitions are correspondingly small. Sméagol uses it to torment his relatives and hides for centuries at the mountains' roots. Bilbo uses the Ring to escape from his obnoxious relatives and neighbors. Frodo falls at the last minute and claims it exactly when the Ring cannot help him. And Sam's dreams of conquest are so petty (an army of enslaved gardeners?) that even he finds it ridiculous and laughs.
The net result is a Subverted Trope: Sauron expected a suitably powerful individual to claim the Ring and try to challenge him outright (at which point he could overpower or outwit them and take it back), but the very pettiness of the evil it worked (or tried to work) through its bearers meant he never got the chance.
Sauron was a sorcerer of immense power who could defeat all the armies in the world if only he had not put his power into the One Ring, which he desperately seeks to regain. Even more so in the backstory, when Sauron was playing The Dragon to Morgoth as the sorcerer lord of the Isle of Werewolves.
Saruman is a wizard who uses his great power to tear down forests to build machines of war and to fortify Isengard for war against Rohan. When Gandalf the Grey learns of his machinations, Saruman overpowers his magic and imprisons him for some time.
The Lord of the Nazgûl (AKA the Witch-King of Angmar) is a powerful sorcerer who brings dread to all around him, a shadow of the death he brings to his enemies.
A place contaminated by the forces of evil is forever tainted, even if it was originally built by one of the Free Peoples (one example is Minas Morgul, formerly a Gondorian city of Minas Ithil, which was so tainted by evil that the Gondorians had to destroy it rather than reclaim after Sauron's defeat). Various attempts to reclaim places such as Moria (a former Dwarven underground kingdom) invariably end in tragedy. No one makes an attempt to claim Saruman's tower of Orthanc after the evil wizard is banished: they just surround Orthanc with Ents and Huorns and make sure no one tries to squat in the tower. Only the places that were merely destroyed by Sauron's minions, not claimed as their own, such as Osgiliath and Fornost, are rebuildable and reclaimable.
It even works if a completely nice structure is built on evil-infested ground. The fortresses built by Gondorians in Mordor to keep Sauron's lackeys from resurging, such as Cirith Ungol and Morannon, eventually withered, became abandoned, and Orcs moved in without any opposition.
Minas Morgul, aka the Tower of Black Sorcery, was built as Minas Ithil (Tower of the Moon) by the exiled Númenóreans to protect Gondor from Sauron's forces. Then the Witch-King of Angmar, The Dragon to Sauron, showed up with an army and made himself at home.
The indestructible tower Orthanc was built by descendants of the Númenóreans as part of Gondor's defensive network, eventually abandoned, and finally given to the wizard Saruman. Pity he turned out to be a Fallen Angel in human form.
The Towers of Teeth at the Black Gate of Mordor were constructed by Gondor after Sauron's defeat to watch against his return. Continuing Gondor's poor track record of Tower maintenance, the armies of the Shadow took them over and incorporated them into Mordor's defences.
Dol Guldur in Mirkwood, formerly a capital of the Forest Elves before Sauron overtook the place in the Second Age. The ruins then became Sauron's hideout during his early return to power before the White Council join forces to drive him out. It later gets razed to the ground by Lady Galadriel when lesser agents of the Shadow move in.
Sauron's personal tower Barad-dûr, raised by his magic in the heart of Mordor to become the greatest stronghold of all Middle-Earth. With the final destruction of Sauron's power, it promptly fell apart.
Exposition of Immortality: Tom Bombadil, Elrond, Treebeard and even Gollum all get in on the remembering things from long, long ago as a means of reminding or showing the reader that they're ancient beings.
External Retcon: The Nursery Rhyme "Hey Diddle Diddle" is given an "original, longer version" in the song "The Man in the Moon Stayed Up Too Late" that Frodo sings in Bree. The deadpan narration has been known to confuse readers as to which version is actually the original.
FaceHeel Turn: Saruman seduced into evil by the perceived superiority of Sauron's power.
The Faceless: The Nazgûl, being invisible to anyone not wearing a great ring or who hasn't lived in the Blessed Realm. When the Witch-King casts back his hood at Minas Tirith, all that's visible is a pair of glowing eyes.
Fainting: Happens to everyone, naturally, but most often to Frodo.
"Facing the Bullets" One-Liner: "Fly, you fools!". Gandalf's last words urging his companions to continue the quest before he falls into the abyss dragged by the Balrog in Moria. The trope is subverted since Gandalf does not die at that point and keeps on fighting, and even when he does die it isn't permanent, but his fellowship and the reader doesn't learn that until much later.
Failure Gambit: Discussed during the Council of Elrond. Gandalf explains how, shortly after the events of The Hobbit, the White Council ejected Sauron from Dol Guldur in Mirkwood. However this seeming defeat was actually a planned move by Sauron back to Mordor.
The Fair Folk: Not exactly — the Elves are all on the side of good — but the Rohirrim think the Lórien elves are these. For that matter, Galadriel herself isn't 100% sure she's not one. Men and Hobbits have an irritating (by Elvish standards) tendency to group elven works and Sauron's dark arts under the umbrella term of "magic". And the Wood Elves, as seen in The Hobbit, are much closer to this than the High Elves. There is also a touch of this trope in the way that non-Elves experience time when visiting Lothlórien.
Fantastic Fragility: The One Ring is a Clingy Macguffinpar excellence, except for that tiny weakness to melting via Mount Doom, though explicitly not dragon-fire, even if said dragon had power on par with the first Worms of Morgoth such as Glaurung or Ancalagon the Black. (The lesser Rings could be melted that way, and indeed four of those that went to the Dwarves suffered just such a fate.)
In portions where Orcs get some dialogue, as opposed to their usual faceless Cannon Fodder role, they are seen to have a great deal of internal racism, with different strains bred for different purposes generally despising one another. This is especially evident in the group that captured Merry and Pippin, since it was a joint effort between Mordor Orcs, Moria "goblins", and the Uruk-Hai of Isengard.
Shortly after the novels' original release, audiences began drawing parallels between them and World War II. J. R. R. Tolkien disliked this interpretation strongly enough that subsequent releases included a foreword that discusses at length all the ways in which the War of the Ring is not like World War II.
On the flipside, the Battle of the Pelennor Fields in The Return of the King shows a great many similarities to the 1683 Battle of Vienna between the Ottoman Empire and the Holy Roman Empire, a long siege that ended in the Turks' rout by the largest cavalry charge in history, led by King Jan III Sobieski of Poland. Meanwhile, Tolkien himself in The History of the Lord of the Rings referenced an account of the Battle of the Catalaunian Plains by the late Roman historian Jordanes, in which Theodoric, King of the Visigoths, was slain in a nevertheless tactically successful battle against the Huns, invaders from the East.
The Witch-King makes a threat of this kind to Eowyn when she gets between him and Theoden.
Witch-King: Come not between the Nazgûl and his prey! Or he will not slay thee in thy turn ... He will bear thee away to the Houses of Lamentation, beyond all darkness, where thy flesh shall be devoured, and thy shrivelled mind be left naked to the Lidless Eye.
The Mouth of Sauron says that this will happen to Frodo if the heroes do not give in to Sauron's demands.
In Rivendell, Gandalf tells Frodo that, had he become a 10th Ringwraith (due to being stabbed with a Morgul Knife), Sauron would have tormented Frodo for eternity for trying to keep the Ring away from him—if anything could compare to the torment of having the Ring taken away by force.
Galadriel's temptation to take the One Ring is dramatized as a One-Winged Angel moment in the book and live-action film. Galadriel imagines herself as a Queen — "not dark, but beautiful" beyond compare. This is also literally the final test for Galadriel: by passing it her exile in Middle-Earth finally ends after 7,000 years.
Sam's temptation at the pass of Cirith Ungol is dramatized in the animated ROTK. Sam imagines himself as Samwise the Strong, who would make the desert of Mordor bloom with gardens.
The Flame of Life: Gandalf identifies himself as "servent of the secret fire, wielder of the flame of Anor" during his confrontation with Durin's Bane, and reveals at the end he has been entrusted with one of the Three, Narya (sometimes called the Ring of Fire). His task on Middle-earth is to encourage, inspire, and fill men with the right sort of fire to confront evil, and after his fall on Durin's Bridge the text describes it as his light going out.
Andúril, Aragorn's sword and an Ancestral Weapon (in the sense that it was reforged from the shards of his ancestor Elendil's sword) is shown bursting into white fire when it is used, for instance when Aragorn hits an orc on the head with it in Moria (and the orc's head explodes) or when he and Éomer sortie against the besiegers of Helm's Deep.
Food Porn: Whenever the hobbits are the viewpoint characters and there is food, it will be described in great detail—as they're from a race of Big Eaters who are getting less than they like, even the elven waybread and ration-cakes of Minas Tirith get this treatment.
Caradhras and Moria. The Fellowship attempts to cross the Pass of Caradhras but is forced to turn back and go through Moria instead.
The wrecked and ruined plain of Dagorlad, which fills a good forty or fifty square miles outside the gates of Mordor. Tolkien gives this forsaken place one of the purplest and most horrendous descriptions in the book:
Frodo looked around in horror. The gasping pools were choked with ash and crawling muds, sickly white and gray, as if the mountains had vomited the filth of their entrails upon the lands about. High mounds of crushed and powdered rock, great cones of earth fire-blasted and poison-stained, stood like an obscene graveyard in endless rows, slowly revealed in the reluctant light. They had come to the desolation that lay before Mordor: the lasting monument to the dark labour of its slaves that should endure when all their purposes were made void; a land defiled, diseased beyond all healing, unless the Great Sea should enter in and wash it with oblivion. "I feel sick," said Sam. Frodo said nothing. Some ugly Truth in Television: Tolkien was describing No-Man's Land between the trenches on the Somme.
The Dead Marshes and Moria are also rather harsh, and both the Old Forest and Fangorn Forest get this label all but smacked onto them.
There's also the Vale of Morgul that grows beautiful but deadly flowers, and where drinking water can drive a person to insanity. Faramir warns Frodo and Sam from drinking from any stream that flows from Imlad Morgul for this reason.
In Book I, at Bree, the hobbits hear that a lot of refugees are coming from the South. They dont pay attention because it seems improbable the Big People will want to live in the Hobbits' small holes and houses. In Rivendell, Elrond wants to send Merry and Pippin back to the Shire because he fears dark influences there. Later, in the wreck of Isengard, they find Saruman had a private stash of Longbottom Leaf. Cue Book VI, "The Scouring of the Shire", where men led by Saruman have taken over the Shire.
Sam's cousin spots a giant walking tree in the Shire, but his tale is considered unbelievable. Later, Merry and Pippin run into a whole society of walking trees (or rather ents).
Frodo is unable to cast the Ring into the fireplace at Bag End when Gandalf is looking for its runes, and later when Gandalf tells him to try and destroy the Ring with a hammer Frodo can't bring himself to do it. Ultimately Frodo is not able to destroy the Ring in Mount Doom when he has to.
Gandalf says the reason Bilbo was able to successfully give up the Ring was that he literally gave it—if he had tried to cast it away instead of making it a present to Frodo, he wouldn't have been able to. Frodo ultimately cannot throw the Ring into Mount Doom.
When Frodo questions Bilbo's mercy with Gollum, Gandalf differs and anticipates Gollum still having a role to play in the quest, somehow. Gollum ultimately destroys the Ring (albeit by accident).
Faramir's words to Samwise are impressively prophetic. "Your land must be a realm of peace and content, and there must gardeners be held in high honour." After returning to the Shire, Sam eventually changes his family name to Gardner and becomes one of the most honored hobbits in history, being elected to the office of Mayor seven consecutive times.
Forgets to Eat: When Frodo jokes about hoping that Sam made plans about inns on their way through Mordor, Sam remembers suddenly that he hadn't eaten or drunk a thing since Frodo was captured. Frodo insists that Sam get some lembas and water into him before they go any further.
Forgot About His Powers: Or rather, about the powers of the magic boats the elves provide. The elves state explicitly that the boats will NOT sink, regardless of the load, and will remain level when left to their own devices. Yet the moment the fellowship enter the boats, they start worrying about the boats lying too low in the water. Also, when one of the boats is later found having gone over a waterfall, and being full of water, yet still afloat, everyone is rather puzzled as to how this is possible, despite being told that the boats would not sink.
Think of what might have been. Dragon fire and savage swords in Eriador, night in Rivendell. There might be no Queen in Gondor. We might now hope to return from the victory here only to ruin and ash. But that has been averted - because I met Thorin Oakenshield one evening on the edge of spring in Bree. A chance-meeting, as we say in Middle-earth
Friend or Foe: The fleet of the Southrons, which was supposed to reinforce the army of Sauron at the battle of the Pelennor, but was captured by Aragorn. Both the Rohirrim and Gondorians thought they were still hostile at first.
From Zero to Hero: Frodo, a normal hobbit living in the peaceful village of the Shire, gets a ring obtained by his uncle Bilbo in The Hobbit. After learning it is an Artifact of Doom smithed by Sauron, this hobbit, accompanied by the Fellowship, goes on a long and dangerous journey so they can destroy the Ring in the fires of Mount Doom, which they succeed at.
Frontline General: Virtually anyone equivalent to a general (Éomer, Théoden, and eventually Aragorn) is only too glad to be right in the thick of it with their men.