The Collaborative International Dictionary of English v.0.48:

Gag \Gag\, n.
   1. Something thrust into the mouth or throat to hinder
      speaking.
      [1913 Webster]

   2. A mouthful that makes one retch; a choking bit; as, a gag
      of mutton fat. --Lamb.
      [1913 Webster]

   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]

The Collaborative International Dictionary of English v.0.48:

Gag \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.
      [1913 Webster]

            The time was not yet come when eloquence was to be
            gagged, and reason to be hood winked. --Maccaulay.
      [1913 Webster]

   2. To pry or hold open by means of a gag.
      [1913 Webster]

            Mouths gagged to such a wideness.     --Fortescue
                                                  (Transl.).
      [1913 Webster]

   3. To cause to heave with nausea.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Gag \Gag\, v. i.
   1. To heave with nausea; to retch.
      [1913 Webster]

   2. To introduce gags or interpolations. See Gag, n., 3.
      [Slang] --Cornill Mag.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gag
    n 1: a humorous anecdote or remark intended to provoke laughter;
         "he told a very funny joke"; "he knows a million gags";
         "thanks for the laugh"; "he laughed unpleasantly at his own
         jest"; "even a schoolboy's jape is supposed to have some
         ascertainable point" [syn: joke, gag, laugh, jest,
         jape]
    2: restraint put into a person's mouth to prevent speaking or
       shouting [syn: gag, muzzle]
    v 1: prevent from speaking out; "The press was gagged" [syn:
         gag, muzzle]
    2: be too tight; rub or press; "This neckband is choking the
       cat" [syn: choke, gag, fret]
    3: tie a gag around someone's mouth in order to silence them;
       "The burglars gagged the home owner and tied him to a chair"
       [syn: gag, muzzle]
    4: make jokes or quips; "The students were gagging during
       dinner" [syn: gag, quip]
    5: struggle for breath; have insufficient oxygen intake; "he
       swallowed a fishbone and gagged" [syn: gag, choke,
       strangle, suffocate]
    6: cause to retch or choke [syn: gag, choke]
    7: make an unsuccessful effort to vomit; strain to vomit [syn:
       gag, heave, retch]

Moby Thesaurus II by Grady Ward, 1.0:

234 Moby Thesaurus words for "gag":
   Oregon boat, acoustic tile, acting, antiknock, asphyxiate, baffler,
   balk, barf, be nauseated, be seasick, be sick, belly laugh, bilbo,
   blue story, boggle, bond, bonds, bottle up, bridle, bring up,
   buffoonery, business, camisole, censor, chains, characterization,
   check, choke, choke off, choke on, chuck up, clamp down on, collar,
   cork, cork up, crack, crack down on, crush, cuffs, curb, cushion,
   damp, damp down, dampener, damper, deflate, dirty joke,
   dirty story, disarm, discourage, disgorge, double entendre,
   drollery, drown, dumbfound, egest, enchain, ethnic joke,
   extinguish, fast one, feed the fish, feel disgust, fetter, fun,
   funny story, gibe, good one, good story, gyves, halter, ham,
   hammy acting, hamper, hamstring, handcuff, handcuffs, heave,
   heave the gorge, hoax, hobble, hobbles, hog-tie, hoke, hokum,
   hold down, hopples, howler, hush, hush-hush, hushcloth,
   impersonation, inhibit, irons, jape, jest, jestbook, jib, joke,
   jump on, keck, keep down, keep under, kill, knock out, laugh,
   leading strings, leash, manacle, mimesis, mimicking, mimicry,
   miming, muffle, muffler, mummery, mute, muzzle, overacting, panic,
   pantomiming, paralyze, patter, performance, performing,
   personation, pillory, play, playacting, playing, point, portrayal,
   pour water on, practical joke, prank, projection, prostrate, puke,
   pun, put down, put to silence, quash, quell, quench, quiet,
   quieten, quietener, quip, regurgitate, reins, reject,
   representation, repress, restrain, restraint, restraints, retch,
   rib tickler, riot, ruse, sally, scream, scruple, shackle, shush,
   shut down on, shy, sick joke, sick up, sicken at, sidesplitter,
   sight gag, silence, silence cloth, silencer, sit down on, sit on,
   slapstick, smash, smother, soft pedal, soft-pedal, sordine,
   sordino, sound-absorbing material, soundproofing,
   soundproofing insulation, sourdine, spew, sport, squash, squelch,
   stage business, stage directions, stage presence, stanch, stick,
   stickle, stifle, still, stocks, stop up, story, straightjacket,
   strain, strait-waistcoat, straitjacket, strangle, stranglehold,
   strike dumb, stultify, stumble, stunt, subdue, suffocate, suppress,
   taking a role, tether, throttle, throw up, trammel, trammels,
   trick, truss up, upchuck, visual joke, vomit, wheeze, wile,
   wisecrack, witticism, wow, yak, yarn, yoke



The Free On-line Dictionary of Computing (30 December 2018):

gag

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

   [Jargon File]