The Collaborative International Dictionary of English v.0.48:

Masquerade \Mas`quer*ade"\, v. i. [imp. & p. p. Masqueraded;
   p. pr. & vb. n. Masquerading.]
   [1913 Webster]
   1. To assemble in masks; to take part in a masquerade.
      [1913 Webster]

   2. To frolic or disport in disquise; to make a pretentious
      show of being what one is not.
      [1913 Webster]

            A freak took an ass in the head, and he goes into
            the woods, masquerading up and down in a lion's
            skin.                                 --L'Estrange.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Masquerade \Mas`quer*ade"\, n. [F. mascarade, fr. Sp. mascarada,
   or It. mascherata. See Mask.]
   [1913 Webster]
   1. An assembly of persons wearing masks, and amusing
      themselves with dancing, conversation, or other
      diversions.
      [1913 Webster]

            In courtly balls and midnight masquerades. --Pope.
      [1913 Webster]

   2. A dramatic performance by actors in masks; a mask. See 1st
      Mask, 4. [Obs.]
      [1913 Webster]

   3. Acting or living under false pretenses; concealment of
      something by a false or unreal show; pretentious show;
      disguise.
      [1913 Webster]

            That masquerade of misrepresentation which
            invariably accompanied the political eloquence of
            Rome.                                 --De Quincey.
      [1913 Webster]

   4. A Spanish diversion on horseback.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Masquerade \Mas`quer*ade"\, v. t.
   To conceal with masks; to disguise. "To masquerade vice."
   --Killingbeck.
   [1913 Webster]

WordNet (r) 3.0 (2006):

masquerade
    n 1: a party of guests wearing costumes and masks [syn:
         masquerade, masquerade party, masque, mask]
    2: a costume worn as a disguise at a masquerade party [syn:
       fancy dress, masquerade, masquerade costume]
    3: making a false outward show; "a beggar's masquerade of
       wealth"
    v 1: take part in a masquerade
    2: pretend to be someone or something that you are not; "he is
       masquerading as an expert on the internet"; "This silly novel
       is masquerading as a serious historical treaty"

Moby Thesaurus II by Grady Ward, 1.0:

208 Moby Thesaurus words for "masquerade":
   Kaffeeklatsch, accouter, act, act a part, act as, act out, acting,
   affectation, ape, aping, appearance, attitudinize, attitudinizing,
   bal, bal costume, bal masque, ball, ballet skirt, barn dance,
   be incognito, blowout, bluff, bluffing, burrow, buskin, camouflage,
   cap and bells, caparison, characterization, cheating, cloak,
   cocktail party, coffee klatch, color, coloring, copy, costume,
   costume party, country dance, cover, cover-up, dance, deception,
   delusion, dinner, dinner party, disappear, disguise, dissemblance,
   dissembling, dissimulation, do, domino, donation party,
   drop from sight, dumb show, embodiment, enact, enacting, enactment,
   entertainment, equip, facade, face, fakery, faking, false air,
   false colors, false face, false front, false show, falsity,
   fancy-dress ball, feigning, feint, festivity, fit, fit out,
   four-flushing, fraud, front, garden party, getup, gilt, gloss,
   go into hiding, go to ground, go underground, habit, hen party,
   hide, hide away, hide out, hole up, hop, house party,
   house-raising, housewarming, humbug, humbuggery, imitate,
   imitation, impersonate, impersonation, imposture, incarnation,
   incognito, lawn party, lie, lie close, lie doggo, lie hid, lie low,
   lie snug, make false pretenses, mask, masked ball, masque,
   masquerade as, masquerade ball, masquerade party, meretriciousness,
   mime, mimesis, mimic, mimicking, mimicry, miming, mixer, motley,
   mummery, ostentation, outfit, outward show, pantomime, pantomiming,
   party, pass for, pass off, perform, performance, performing,
   personate, personation, personification, play, play a part,
   play peekaboo, playacting, playing, portrayal, pose, pose as,
   posing, posture, pretend to be, pretense, pretension, pretext,
   prom, promenade, protective coloration, put-on, record hop,
   remain anonymous, representation, retire from sight, rig, rig out,
   rig up, seeming, semblance, sham, shindig, shindy, show, shower,
   simulacrum, simulate, simulation, sit tight, smoke screen, smoker,
   sock, speciousness, square dance, stag, stag dance, stag party,
   stay in hiding, subterfuge, suit, surprise party, take cover,
   take off, tea dance, the dansant, tights, turn out, tutu, uniform,
   varnish, veil, visor, vizard, vizard mask, wear a mask,
   window dressing