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->Yes, Shaniqua. She was a dominatrix. Because, you know, wrestling needs dominatrixs.
->Dominatrixes?
->Dominatrixi?
->Whatever.
-->--RD Reynolds, ''Wrestlecrap''

Part of what you know when you know a language is how to make your words fit into a grammatical system. This can be fairly simple, as in English (the odd -s here, the odd -ed there) or fairly complex, as in the Russian case system. One thing all systems have in common though, is that they work all the time. For every singular, there is a plural.(Though there are [[http://en.wikipedia.org/wiki/Mass_noun cases where there is neither]].) It might be regular (trope, tropes) or irregular (goose, geese), but you know it's there and you know what it is.

...until you find yourself needing to talk about octopuses...octopus...octopi- no, [[DogLatin that's Latin]]...octopodes? Ugh, now this is going to bother me all day.[[note]]The fact that [[https://en.wiktionary.org/wiki/octopus#Noun all three plurals]] given in this example are considered correct doesn't help.[[/note]]

Sometimes you go for a plural and...there isn't one. Maybe it's an unfamiliar word, maybe you've heard different options and don't know what to pick, maybe language is just screwing with you. Whatever the reason, it feels so overwhelmingly '''wrong''' that you have to stop and talk about it. Almost always derails the conversation at hand, and may be the equivalent of a LogicBomb to a GrammarNazi.

TruthInTelevision. Related to the phenomenon of "paradigmatic gapping" in RealLife, where a grammatical form that logically should exist just...doesn't.[[labelnote:case in point]]The proverbial example in English is the verb "can", which can be used in the present or the past, but not in any other tenses. You just can't say "I will can do X", you need to use something like "will be able to" instead.[[/labelnote]]

Note: This is crucially not a trope used by {{Funny Foreigner}}s. It is confusion about a speaker's '''own language''' (and the need to stop and work it out) and usually not caused by ignorance or BookDumb (although expect a character beset by SesquipedalianLoquaciousness to be immune). See {{Pluralses}}

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!!Examples

[[AC: FanWorks]]
* In ''[[http://sam-storyteller.dreamwidth.org/2005/07/10/ Cartographer's Craft]]'', a ''Franchise/HarryPotter'' fanfic by copperbadge, Hermione insists on using "Horcruces" as the plural of "Horcrux" instead of "Horcruxes", to everyone else's chagrin.
* A minor RunningGag in ''Fanfic/ItsADangerousBusinessGoingOutYourDoor'' involves Rarity automatically correcting Rainbow Dash whenever the latter says "pegasuses" instead of "pegasi". Applejack eventually gets sick of the argument and tells Rainbow Dash to use "pegasi" and Rarity to stop being so uptight about it.

[[AC: {{Film}}]]
* ''Film/MysteryMen'': Captain Amazing comments to Casanova Frankenstein that they have always been each other's greatest "nemisises..nemisi..." (It's "nemeses," as Casanova points out.)

[[AC: {{Literature}}]]
* In ''Literature/GoodOmens'', Shadwell's instructions to Newt are to search for:
--> 1. [[BurnTheWitch Witches.]]\\
2. Unexplainable Phenomenons. Phenomenatrices. Phenomenice. Things, ye ken well what I mean.
* Since the climax of ''Literature/ThePyrates'' occurs at the aptly-named Octopus Rock, the inevitable confusion ensues. Antihero Colonel Blood uses the incorrect Latinate plural "octopi," and smarmy hero Captain Avery offers him the correct (though antiquated) Greek "octopods" or "octopodes." Largely out of contrariness, Blood elects to go with "octopussies."

[[AC: LiveActionTV]]
* ''TheBradyBunch'': The [[PlotThreads B Plot]] of the episode "The Personality Kid" concerns Bobby & Cindy going ape-shit over safety. The following concerns some electrical outlets in the kitchen, which have so many extensions & multi-prongs plugged in that one is referred to as an "octopus."
-->''(Bobby hands Carol a new plug)''\\
'''Carol:''' Now I hope these are the right plugs.\\
'''Bobby:''' Just the kind the teacher said to get instead of that old octopus.\\
'''Alice:''' Do you know that all last night I dreamed about octopuses?...Octopussys?...Octopi?
* In ''Series/BuffyTheVampireSlayer'':
** Riley comments that, after falling in with the main characters, he suddenly finds himself needing to know the [[TheWorldIsAlwaysDoomed plural of "apocalypse"]]. (It's "apocalypses", by the way).
** In the 6th-season's "Gone", [[BigBadWannabe Warren]] declares to Buffy that "We are your arch-nemesises...ses." When they fail to open their escape door, Buffy mockingly says to Willow: "I give you my arch-nemesis...ses...ses." It became a BrickJoke when a vampire the next season said it was "nemeses," which Buffy duly noted.
** In the seventh season, Willow tries to assemble the ingredients for a spell:
-->'''Willow:''' OK, I got my tumbleweed, my eggs, got my chrysalises...chrysali...? My [[BuffySpeak butterfly transformer pods]].
* The girls of ''Series/ICarly'' spend a fairly large amount of "iGo to Japan" arguing of the current plural of the word "possum".
* There is a variant of this in ''Series/ArrestedDevelopment''. GOB has just chipped a tooth, causing him to whistle his S's, and is dense enough that he think he can avoid using an "S" by switching to a different plural noun.
-->'''GOB:''' I have a few terms (whistle)... I mean conditions (whistle)... I have one term and one condition.
* In the ''Series/HoneyIShrunkTheKids'' episode "From Honey, with Love", the family briefly gets into an argument over the correct plural of "moose". Nick produces the correct answer: "The plural of 'moose' is 'moose'. Like 'sheep', or 'deer'."
* ''Series/TheBigBangTheory'': Raj tells Leonard and Howard that he hopes they fall down and break their 'coccyxes'. Sheldon corrects him that the plural of 'coccyx' is 'coccyges'.

[[AC: {{Music}}]]
* Used in the NoveltySong "I Want a Hippopotomus for Christmas."
-->I want a hippopotamus for Christmas\\
Only a hippopotamus will do\\
No crocodiles or rhinoceroseses\\
I only like hippopotamuseses\\
And hippopotamuses like me too!
* The AllanSherman song "One Hippopotami" (a parody of "What Kind Of Fool Am I?") is half this trope and half "pair" puns.
-->One hippopotami cannot get on a bus\\
Because one hippopotami is two hippopotamus\\
And if you have two goose, that makes one geese\\
A pair of mouse is mice, a pair of moose is meese

[[AC: TabletopGames]]
* The Tyranids in ''TabletopGame/{{Warhammer 40000}}'' have the Carnifex. Good luck getting the fans to agree on a plural.
** ...[[CompletelyMissingThePoint Bad news]]?
** The plural of "codex" (the name for a faction army book) is another one. Although "codexes" is used officially, many prefer the correct Latin form "codices" (and, likewise, will use "carnifices" to pluralise carnifex, also correct Latin). Given that many things in 40k get pseudo-Latin names that don't abide by traditional Latin grammatical rules, this might actually be less appropriate.
* In ''TabletopGame/MagicTheGathering'', a powerful mana-generating card is the Mox (Mox Ruby, Mox Sapphire, and so forth). Traditionally, the plural is "Moxen".

[[AC: VideoGames]]
* ''VideoGame/KingdomOfLoathing'' tends to have a lot of fun with plurals, with "box" becoming "[[Creator/BrianRegan boxen]]", "kiwi" becoming "kiwus", "fruit basket" becoming [[FruitsBasket "fruits basket"]], and "liar's pants" becoming [[TheLordOfTheRings "liar's pantses, precious"]]. Items which you can only legitimately have one of tend to have plurals calling NoFairCheating; for example, the plural of "Staff of Ed" is "Staves of Ed, you dirty exploiter you".
* Nobody in the ''VideoGame/{{Freespace}}'' fandom is sure what the plural of "Sathanas" is supposed to be (given that it's an alternate name for {{Satan}}, it probably doesn't have one). Expect to see "Sathanai", "Sathanes", or "[[RuleOfFunny Sathanaseses]]" depending on the fan in question. The game itself avoids the issue by always referring to that ship class as "Sathanas juggernaut(s)".
* At one point in ''VideoGame/AssassinsCreedII'', Desmond loses his focus when wondering what the plural for "animus", the machines that allow him to experiece his ancestors' lives, is.
* ''VideoGame/{{Xenoblade}}'' has nearly every race use the same word for their singlar and plural forms. For instace, the singular of [[HumanAliens Homs]] is still Homs; while the plurals for the [[RidiculouslyCuteCritter Nopon]] and [[OurElvesAreBetter High Entia]] are the same. Only the extinct Giants have their singular form be the more obvious Giant.

[[AC: WesternAnimation]]
* In one episode of ''WesternAnimation/KimPossible'' Drakken builds a machine that drains a lake, and he comments on the machine not filtering out all the "fishes". This launches an argument between him and Shego about what the plural of fish is. Shego tells him that both fishes and fish are correct plurals for the word.
* In the ''WesternAnimation/PhineasAndFerb'' episode "Greece Lightning", the narrator of an educational filmstrip is unsure how to refer to [[EverythingsBetterWithPlatypus platypi]]. Platypuses. Platypeople?
* In ''WesternAnimation/TeenTitans'', Control Freak gets stuck on the plural for "nemesis" in one episode.
* In ''WesternAnimation/TheSimpsons'', Principal Skinner at one point refers to ''"hypothetical dogs and poni"''.
* ''WesternAnimation/MyLittlePonyFriendshipIsMagic'' took a while to commit to a standard plural form of "pegasus", initially copping out and using "pegasus ponies" before settling on "pegasi". In "Hearth's Warming Eve", Chancellor Puddinghead, as played by Pinkie Pie in the Hearth's Warming Eve pageant, gets confused and calls them "pegasus-es-es."
* An episode of ''WesternAnimation/{{Hercules}}'' involving the crew of the Argo had an argument over the plural of {{cyclops}}, with most of the suggestions being similar to plurals of "octopus". Ironically, the one a person stated most authoritative ("cyclopi") is the only one that ''wasn't'' right.
* The Sultan's advisors in ''WesternAnimation/HugoTheHippo'' can't agree on the plural of "hippopotamus", suggesting "hippopotamuses", "hippopotami", and even "hippopotamus", before the Sultan cuts the Gordian knot and calls them "hippos".

[[AC: Jokes[=/=]RealLife]]
* Some Russian jokes deal with the unpredictable nature of Russian plural nouns. An example from {{Wikipedia}}:
-->The genitive plural of a noun (used with a numeral to indicate five or more of something, as opposed to the dual, used for two, three, or four, see Russian nouns) is a rather unpredictable form of the Russian noun, and there are a handful of words which even native speakers have trouble producing this form of (either due to rarity or an actual lexical gap). A common example of this is kocherga (fireplace poker). The joke is set in a Soviet factory. Five pokers are to be requisitioned. The correct forms are acquired, but as they are being filled out, a debate arises: what is the genitive plural of kocherga? Is it Kocherg? Kocherieg? Kochergov?... One thing is clear: a form with the wrong genitive plural of kocherga will bring disaster from the typically-pedantic bureaucrats. Finally, an old janitor overhears the commotion, and tells them to send in two separate requisitions: one for two kochergi and another for three kochergi. In some versions, they send in a request for 4 kochergi and one extra to find out the correct word, only to receive back "here are your 4 kochergi and one extra."
* There's an old Italian joke where a man doesn't know if the plural for "Belga" (a person from Belgium) is "Belghi" or "Belgi". He eventually resorts to write down "Un Belga. Anzi due!" (One Belgian. I mean, two.)
* Creator/BrianRegan has a routine built around this trope. It starts with "boxen" (like oxen) of donuts and just snowballs from there.
** Richard Lederer's "[[http://findarticles.com/p/articles/mi_go2573/is_4_29/ai_n29150810/ Foxen in the Henhice]]" is based around the same concept.
* There's a joke about someone shipping a pair of mongooses to a zoo and being unsure of what the plural of "mongoose" is. They start out writing a note referring them to "mongooses", then try "mongeese", and eventually resort to writing "Enclosed is the mongoose you ordered. Also enclosed is the other mongoose you ordered".
* Hacker jargon plays with this a lot; one of the more prominent examples is the old Digital VAX minicomputer. Although not completely universal, the plural [=VAXen=] is common.
* Weetabix. Is the plural Weetabix or Weetabices?

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[[spoiler:Incidentally: '''''Octopodes'''''. It's from the Greek.]]

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