The Collaborative International Dictionary of English v.0.48:

Gull \Gull\ (g[u^]l), v. t. [imp. & p. p. Gulled (g[u^]ld); p.
   pr. & vb. n. Gulling.] [Prob. fr. gull the bird; but cf.
   OSw. gylla to deceive, D. kullen, and E. cullibility.]
   To deceive; to cheat; to mislead; to trick; to defraud.
   [1913 Webster]

         The rulgar, gulled into rebellion, armed. --Dryden.
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         I'm not gulling him for the emperor's service.
                                                  --Coleridge.
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The Collaborative International Dictionary of English v.0.48:

Gull \Gull\, n.
   1. A cheating or cheat; trick; fraud. --Shak.
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   2. One easily cheated; a dupe. --Shak.
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The Collaborative International Dictionary of English v.0.48:

Gull \Gull\, n. [Of Celtic origin; cf. Corn. gullan, W. gwylan.]
   (Zool.)
   One of many species of long-winged sea birds of the genus
   Larus and allied genera.
   [1913 Webster]

   Note: Among the best known American species are the herring
         gull (Larus argentatus), the great black-backed gull
         (L. murinus) the laughing gull (L. atricilla), and
         Bonaparte's gull (L. Philadelphia). The common
         European gull is Larus canus.
         [1913 Webster]

   Gull teaser (Zool.), the jager; -- also applied to certain
      species of terns.
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WordNet (r) 3.0 (2006):

gull
    n 1: a person who is gullible and easy to take advantage of
         [syn: chump, fool, gull, mark, patsy, fall guy,
         sucker, soft touch, mug]
    2: mostly white aquatic bird having long pointed wings and short
       legs [syn: gull, seagull, sea gull]
    v 1: make a fool or dupe of [syn: fool, gull, befool]
    2: fool or hoax; "The immigrant was duped because he trusted
       everyone"; "You can't fool me!" [syn: gull, dupe,
       slang, befool, cod, fool, put on, take in, put
       one over, put one across]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "gull":
   babe, bamboozle, beat, befool, beguile, beguile of, betray, bilk,
   bluff, boob, bunco, burn, cajole, cheat, cheat on, chicane, chisel,
   chouse, chouse out of, chump, cinch, circumvent, cog, cog the dice,
   con, conjure, cozen, credulous person, crib, cull, deceive,
   defraud, delude, diddle, do in, do out of, double-cross, dupe,
   easy mark, easy pickings, euchre, fall guy, finagle, fish, flam,
   fleece, flimflam, fob, fool, forestall, fudge, gammon, get around,
   gobe-mouches, gouge, greener, greenhorn, greeny, gudgeon, gyp,
   have, hoax, hocus, hocus-pocus, hoodwink, hornswaggle, humbug,
   infatuate, innocent, juggle, leadpipe cinch, let down, mock,
   monkey, mulct, outmaneuver, outreach, outsmart, outwit, overreach,
   pack the deal, patsy, pigeon, play one false, plaything,
   practice fraud upon, prize sap, pushover, put on,
   put something over, rook, sap, saphead, scam, schlemiel, screw,
   sell gold bricks, shave, shortchange, sitting duck, snow,
   stack the cards, stick, sting, stooge, string along, stultify,
   sucker, swindle, take a dive, take in, thimblerig, throw a fight,
   toy, trick, trusting soul, two-time, victim, victimize