Quack

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