Quack

quack
    adj 1: medically unqualified; "a quack doctor"
    n 1: an untrained person who pretends to be a physician and who
         dispenses medical advice
    2: the harsh sound of a duck
    v 1: utter quacking noises; "The ducks quacked"
    2: act as a medical quack or a charlatan
    

Quack \Quack\, n.
   1. The cry of the duck, or a sound in imitation of it; a
      hoarse, quacking noise. --Chaucer.
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   2. [Cf. {Quacksalver}.] A boastful pretender to medical
      skill; an empiric; an ignorant practitioner.
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   3. Hence, one who boastfully pretends to skill or knowledge
      of any kind not possessed; a charlatan.
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            Quacks political; quacks scientific, academical.
                                                  --Carlyle.
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Quack \Quack\, a.
   Pertaining to or characterized by, boasting and pretension;
   used by quacks; pretending to cure diseases; as, a quack
   medicine; a quack doctor.
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Quack \Quack\, v. i. [imp. & p. p. {Qvacked}; p. pr. & vb. n.
   {Quacking}.] [Of imitative origin; cf. D. kwaken, G. quacken,
   quaken, Icel. kvaka to twitter.]
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   1. To utter a sound like the cry of a duck.
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   2. To make vain and loud pretensions; to boast. " To quack of
      universal cures." --Hudibras.
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   3. To act the part of a quack, or pretender.
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QUACK. One, who, without sufficient knowledge, study or previous 
preparation, and without the diploma of some college or university, 
undertakes to practice medicine or surgery, under the pretence that he 
possesses secrets in those arts. 
     2. He is criminally answerable for his unskillful practice, and also, 
civilly to his patient in certain cases. Vide Mala praxis; Physician. 
    

75 Moby Thesaurus words for "quack":
      blagueur, bluff, bluffer, cackle, call, carol, caw, charlatan,
      charlatanic, charlatanish, chatter, cheep, chirk, chirp, chirr,
      chirrup, chitter, chuck, clack, cluck, cock-a-doodle-doo, coo,
      counterfeit, counterfeiter, croak, cronk, crow, cuckoo, drum, fake,
      faker, fourflusher, fraud, fraudulent, gabble, gaggle, gobble,
      guggle, honk, hoo, hoot, horse doctor, humbug, impersonator,
      impostor, malingerer, medicaster, medicine man, medicine monger,
      mountebank, peep, phony, pip, pipe, poser, poseur, pretender,
      quackish, quacksalver, quackster, ringer, roll, saltimbanco, scold,
      sham, shammer, simulator, sing, squawk, trill, tweet, twit,
      twitter, warble, whistle