Definition of quacks:
(n) :
The sound made by a duck.
(v) :
To make a noise like a duck.
(n) :
(derogatory) A fraudulent healer, especially a bombastic peddler in worthless treatments, a doctor who makes false diagnoses for monetary benefit, or an untrained or poorly trained doctor who uses fraudulent credentials to attract patients
(n) :
(figuratively, derogatory) Any similar charlatan or incompetent professional.
(n) :
(humorous slang, mildly derogatory) Any doctor.
(v) :
To practice or commit quackery (fraudulent medicine).