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.][1913 Webster]
1. To utter a sound like the cry of a duck.[1913 Webster]
2. To make vain and loud pretensions; to boast. “ To quack of universal cures.” Hudibras.[1913 Webster]
3. To act the part of a quack, or pretender.[1913 Webster]
Quack, n. 1. The cry of the duck, or a sound in imitation of it; a hoarse, quacking noise. Chaucer.[1913 Webster]
2. [Cf. Quacksalver.] A boastful pretender to medical skill; an empiric; an ignorant practitioner.[1913 Webster]
3. Hence, one who boastfully pretends to skill or knowledge of any kind not possessed; a charlatan.[1913 Webster]
Quacks political; quacks scientific, academical.
Quack, a. Pertaining to or characterized by, boasting and pretension; used by quacks; pretending to cure diseases; as, a quack medicine; a quack doctor.[1913 Webster]