Definition of quack

What does the word quack mean?

• part of speech: verb intransitive

  (Utter) harsh sound made by ducks; talk loudly& foolishly; q.-q. (nursery), duck. [Dutch]

• part of speech: noun

  Ignorant pretender to skill esp. in medicine or surgery, one who offers wonderful remedies or devices, charlatan, (often attrib., as q. doctor, remedies); hence quackery (4) n., quackish a., (Vb) play the q.; talk pretentiously; puff or advertise (cure &c.).