1. [n]  restraint put into a person's mouth to prevent speaking or shouting
2. [n]  a humorous anecdote or remark
3. [v]  make an unsuccessful effort to vomit; strain to vomit
4. [v]  cause to retch or choke
5. [v]  struggle for breath; have insufficient oxygen intake; "he swallowed a fishbone and gagged"
6. [v]  make jokes or quips; "The students were gagging during dinner"
7. [v]  be too tight; rub or press; "This neckband is choking the cat"
8. [v]  prevent from speaking

Gag
Gag

more details ...

1. \Gag\, v. t. [imp. & p. p. {Gagged}; p. pr. & vb. n.
   {Gagging}.] [Prob. fr. W. cegio to choke or strangle, fr. ceg
   mouth, opening, entrance.]
   1. To stop the mouth of, by thrusting sometimes in, so as to
      hinder speaking; hence, to silence by authority or by
      violence; not to allow freedom of speech to. --Marvell.
            The time was not yet come when eloquence was to be
            gagged, and reason to be hood winked. --Maccaulay.
   2. To pry or hold open by means of a gag.
            Mouths gagged to such a wideness.     --Fortescue
                                                  (Transl.).
   3. To cause to heave with nausea.
   

2. \Gag\, v. i.
   1. To heave with nausea; to retch.
   2. To introduce gags or interpolations. See {Gag}, n., 3.
      [Slang] --Cornill Mag.
   

3. \Gag\, n.
   1. Something thrust into the mouth or throat to hinder
      speaking.
   2. A mouthful that makes one retch; a choking bit; as, a gag
      of mutton fat. --Lamb.
   3. A speech or phrase interpolated offhand by an actor on the
      stage in his part as written, usually consisting of some
      seasonable or local allusion. [Slang]
   {Gag rein} (Harness), a rein for drawing the bit upward in
      the horse's mouth.
   {Gag runner} (Harness), a loop on the throat latch guiding
      the gag rein.
   

Equivalent to choke, but connotes more disgust. "Hey, this is Fortran code. No wonder the C compiler gagged." See also barf.

[Jargon File]

1. A macromolecule found on the surface of eukaryotic cells which is thought to play a role in the cell's recognition of other cells or of a substrate. It consists of a network of long, branched chains made up of repeating units of disaccharides which contain amino groups.
2. A protein component of the capsid of a retrovirus which can act as group-specific antigens to the host.