The Collaborative International Dictionary of English v.0.48:

Charlatan \Char"la*tan\, n. [F. charlatan, fr. It. ciarlatano,
   fr. ciarlare to chartter, prate; of imitative origin; cf. It.
   zirlare to whistle like a thrush.]
   One who prates much in his own favor, and makes unwarrantable
   pretensions; a quack; an impostor; an empiric; a mountebank.
   [1913 Webster] Charlatanic

WordNet (r) 3.0 (2006):

charlatan
    n 1: a flamboyant deceiver; one who attracts customers with
         tricks or jokes [syn: mountebank, charlatan]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "charlatan":
   blagueur, bluff, bluffer, charlatanic, charlatanish, fake, faker,
   fourflusher, fraud, horse doctor, humbug, impersonator, impostor,
   malingerer, medicaster, medicine man, medicine monger, mountebank,
   phony, poser, poseur, pretender, quack, quackish, quacksalver,
   quackster, ringer, saltimbanco, sham, shammer