The Collaborative International Dictionary of English v.0.48:

Humbug \Hum"bug`\, n. [Prob. fr. hum to impose on, deceive + bug
   a frightful object.]
   1. An imposition under fair pretenses; something contrived in
      order to deceive and mislead; a trick by cajolery; a hoax.
      [1913 Webster]

   2. A spirit of deception; cajolery; trickishness.
      [1913 Webster]

   3. One who deceives or misleads; a deceitful or trickish
      fellow; an impostor. --Sir J. Stephen.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Humbug \Hum"bug`\, v. t. [imp. & p. p. Humbugged; p. pr. & vb.
   n. Humbugging.]
   To deceive; to impose; to cajole; to hoax.
   [1913 Webster]

WordNet (r) 3.0 (2006):

humbug
    n 1: pretentious or silly talk or writing [syn: baloney,
         boloney, bilgewater, bosh, drool, humbug,
         taradiddle, tarradiddle, tommyrot, tosh, twaddle]
    2: communication (written or spoken) intended to deceive [syn:
       humbug, snake oil]
    3: something intended to deceive; deliberate trickery intended
       to gain an advantage [syn: fraud, fraudulence, dupery,
       hoax, humbug, put-on]
    v 1: trick or deceive

Moby Thesaurus II by Grady Ward, 1.0:

192 Moby Thesaurus words for "humbug":
   absurdity, acting, affectation, amphigory, appearance,
   attitudinizing, babble, babblement, balderdash, balls, baloney,
   bamboozle, beguile, betray, bibble-babble, blabber, blague,
   blagueur, blather, blatherskite, bluff, bluffer, bluffing, bombast,
   bosh, bull, bullshit, bunk, bunkum, cajole, charlatan,
   charlatanism, charlatanry, cheat on, cheating, circumvent,
   claptrap, color, coloring, conjure, crap, deceive, deception,
   delude, delusion, diddle, disguise, dissemblance, dissembling,
   dissimulation, double-cross, double-talk, drivel, drool, dupe,
   eyewash, facade, face, fake, fakement, faker, fakery, faking,
   false air, false front, false show, falsity, feigning, feint,
   fiddle-faddle, fiddledeedee, flam, flapdoodle, flimflam, flummery,
   folderol, forestall, four-flushing, fourflusher, fraud, front,
   fudge, fustian, gabble, galimatias, gammon, get around, gibber,
   gibberish, gibble-gabble, gilt, gloss, gobbledygook, gull, gyp,
   hoax, hocus-pocus, hogwash, hoke, hokum, hooey, hornswaggle,
   humbuggery, impersonator, impostor, imposture, jabber, jargon,
   jiggery-pokery, juggle, let down, malarkey, malingerer, masquerade,
   meretriciousness, mislead, mock, moonshine, mountebank,
   mumbo jumbo, narrishkeit, niaiserie, nonsense, ostentation,
   outmaneuver, outreach, outsmart, outward show, outwit, overreach,
   pack of nonsense, palaver, phony, piffle, pigeon, play one false,
   playacting, pose, poser, poseur, posing, posture, prate, prattle,
   pretender, pretense, pretension, pretext, put something over,
   quack, quackery, quackishness, quackism, quacksalver, quackster,
   rant, representation, rigamarole, rigmarole, ringer, rip-off,
   rodomontade, rot, rubbish, saltimbanco, seeming, sell, semblance,
   sham, shammer, show, simulacrum, simulation, skimble-skamble, snow,
   speciousness, spoof, string along, stuff and nonsense,
   stultiloquence, take in, trash, trick, trumpery, twaddle, twattle,
   twiddle-twaddle, two-time, vaporing, varnish, waffling,
   window dressing