Quack, n. 1. The cry of the duck, or a sound in imitation of it; a hoarse, quacking noise. Chaucer.
2. [Cf. Quacksalver.] A boastful pretender to medical skill; an empiric; an ignorant practitioner.
3. Hence, one who boastfully pretends to skill or knowledge of any kind not possessed; a charlatan.
Quacks political; quacks scientific, academical. Carlyle.