Dictionary

The sound made by a duck.

Example: Did you hear that duck make a quack?

To make a noise like a duck.

Example: Do you hear the ducks quack?

A fraudulent healer or incompetent professional; especially, a doctor of medicine who makes false diagnoses or inappropriate treatment; an impostor who claims to have qualifications to practice medicine.

Example: That doctor is nothing but a lousy quack!

A charlatan.

A doctor.

To practice or commit quackery (fraudulent medicine).

To make vain and loud pretensions.

Falsely presented as having medicinal powers.

Example: Don't get your hopes up; that's quack medicine!