Meaning Of Quack

v. i.

To utter a sound like the cry of a duck.
v. i.

To make vain and loud pretensions; to boast.
v. i.

To act the part of a quack, or pretender.
n.

The cry of the duck, or a sound in imitation of it; a hoarse, quacking noise.
n.

A boastful pretender to medical skill; an empiric; an ignorant practitioner.
n.

Hence, one who boastfully pretends to skill or knowledge of any kind not possessed; a charlatan.
a.

Pertaining to or characterized by, boasting and pretension; used by quacks; pretending to cure diseases; as, a quack medicine; a quack doctor.