!

May derive from a Latin Io, with the I written over the o, placed at the end of an exclamation to mark it as such. The Io may either be an abbreviation for interiectiō (“interjection”), or else the interjection iō (“hey!”).[1]

!

1. Denoting excitement, surprise, or shock.
   1. Expresses excitement, anger or other emotion.

      What a beautiful day!

      • 2007, J. K. Rowling, Harry Potter e as Relíquias da Morte [Harry Potter and the Deathly Hallows] (Harry Potter; 7), Rio de Janeiro: Rocco, →ISBN, page 369:

        Seu macaquinho imundo!

        You filthy little monkey!

   2. Replacing a period at the end of a declarative sentence.

      I had no idea!

   3. Following a question mark at the end of an interrogative sentence.

      How is that possible?!

   4. At the end of an interjection that is set off by dashes or parentheses.

      After he finished his drink — his fifth! — he left the room.

   5. In parentheses; see (!).

      After he finished his fifth drink (!), he left the room.

   6. (comics) Used in some comics instead of the period (.), ending all sentences, except those that use question marks, ellipses, etc.
   7. (comics, video games) Used by itself to convey that a character is surprised at something.

      Character #1: "The zombie is right behind you!"

      Character #2: "!"

      • 1996, Pokémon Red and Blue (video game)

        ! [indicates that another trainer noticed the player character, prompting a battle between them]

      • 2015 September 15, Toby Fox, Undertale (video game), Linux, Microsoft Windows, OS X:

        ! [indicates a random encounter with a monster]

2. (botany) Placed after a herbarium abbreviation to indicate that the mentioned material held there has been examined directly by the author.
   • 2008, June, A Michele Funston, "Taxonomic Revision of Roldana (Asteraceae: Senecioneae), a Genus of the Southwestern U.S.A., Mexico, and Central America", Annals of the Missouri Botanical Garden, volume 95, issue 2, page 307:

     TYPE: Mexico. Nayarit: Tepic, 10 Feb. 1927, Marcus E. Jones 23357 (holotype, POM not seen; isotype, US!).

3. (Internet, fandom slang) Used to join a descriptor with its referent; usually a character or relationship.

   She particularly prefers to read fanfiction about hurt!Spock.

• Its English name is variously exclamation mark, exclamation point, exclamation, ecphoneme, or, in computing contexts, shriek, bang or pling.
• In its use to denote excitement, surprise, or shock, it is sometimes repeated for additional emphasis, as in "!!", "!!!", "??!!!", or the like.

Punctuation

!

1. (mathematics) The factorial: the result of a multiplication of all integers from 1 to the given number.

   5! = 5 × 4 × 3 × 2 × 1 = 120

   "five factorial equals 120"

2. (chess) Indicates a good move.
   • 1983, Claude Santoy, Échecs et maths, Marabout, →ISBN, page 134:

     (Fb4! 10.c3 suivi de De7 eut été plus précis)

     (Bb4! 10.c3 followed by Qe7 would have been more efficient)

3. (computing, in many programming languages) A Boolean negation, the not operator, serving to invert the truth value of what follows.
4. (computing, e-mail) Formerly used as a separator between hostnames in an e-mail address for the purpose of routing a message (called bang path notation).
5. (computing, IRC) Used as a separator between a user's nickname and ident.

• ՜ (Armenian)

!

1. in glosses, marks a word as imperative

   manĝi, manĝu, manĝis "eat, eat!, ate"

!

1. (obsolescent) Used at the end of a salutation line of a letter

   Lieber Hans!

   Dear Hans,