Definition 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.