to utter a sound like the cry of a duck.-to make vain and loud pretensions; to boast.-to act the part of a quack, or pretender.-the cry of the duck, or a sound in imitation of it; a hoarse, quacking noise.-a boastful pretender to medical skill; an empiric; an ignorant practitioner.-hence, one who boastfully pretends to skill or knowledge of any kind not possessed; a charlatan.-pertaining to or characterized by, boasting and pretension; used by quacks; pretending to cure diseases; as, a quack medicine; a quack doctor.