When anyone shouts a single word (repeat, one word) hard and loud, for various reasons, as long as the reason is other than actually needing to shout (noisy room, someone is far away, barking out orders).

Often done for dramatic effect, actually Melodramatic effect, to the point this is rarely played straight anyway, due to the Narm potential.

Often done with a Skyward Scream, if the word is someone's name.

In case you hadn't guessed it, Big No and Big Yes are SubTropes of this.

Compare GASP!, Say My Name.

Not to be confused with Big Words.

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Examples:

• KHAAAAAAAN!
  • SPOCK!
• "SUUUURGE!" from Coca-Cola's attempt to enter the Mountain Dew market.