Quack (v. i.) : To utter a sound like the cry of a duck.
Quack (v. i.) : To make vain and loud pretensions; to boast.
Quack (v. i.) : To act the part of a quack, or pretender.
Quack (n.) : The cry of the duck, or a sound in imitation of it; a hoarse, quacking noise.
Quack (n.) : A boastful pretender to medical skill; an empiric; an ignorant practitioner.
Quack (n.) : Hence, one who boastfully pretends to skill or knowledge of any kind not possessed; a charlatan.
Quack (a.) : Pertaining to or characterized by, boasting and pretension; used by quacks; pretending to cure diseases; as, a quack medicine; a quack doctor.