The Collaborative International Dictionary of English v.0.48:

Poseur \Po`seur"\, n. masc.; pl. Poseurs, Poseuse \Po`seuse"\,
   n. fem.; pl. Poseuses, [F.]
   A person who poses or attitudizes, esp. mentally.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

poseur
    n 1: a person who habitually pretends to be something he is not
         [syn: poseur, poser]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "poseur":
   ape, attitudinarian, attitudinizer, blagueur, bluff, bluffer,
   charlatan, conformist, copier, copycat, copyist, counterfeiter,
   cuckoo, dissembler, dissimulator, echo, echoer, echoist,
   exhibitionist, fake, faker, forger, fourflusher, fraud, humbug,
   hypocrite, imitator, impersonator, impostor, malingerer,
   masquerader, mime, mimer, mimic, mimicker, mocker, mockingbird,
   monkey, mountebank, parrot, phony, plagiarist, poll-parrot, polly,
   polly-parrot, poser, posture maker, posturer, posturist, pretender,
   quack, quacksalver, quackster, ringer, saltimbanco, sham, shammer,
   sheep, show-off, simulator, striker of poses