verb

• (intransitive) Of a queen bee: to make a high-pitched sound during certain stages of development.

noun

• (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
  "That doctor is nothing but a lousy quack!"
• (figuratively, derogatory) Any similar charlatan or incompetent professional.
  "The very quaik of faſhions, the very hee that / VVeares a Steletto on his chinne."
• (humorous slang, mildly derogatory) Any doctor.
  "That quack wants me to quit smoking, eat less, and start exercising. The nerve!"

verb

• (obsolete) To make vain and loud pretensions.
  "Seek out for Plants with Signatures To Quack of Universal Cures"