Collins COBUILD Advanced Learner's English Dictionary - quack

(quacks, quacking, quacked) 1. If you call someone a quack or a quack doctor, you mean that they claim to be skilled in medicine but are not. I went everywhere for treatment, tried all sorts of quacks. N-COUNT: oft N n c darkgreen]disapproval 2. Quack remedies or quack cures are medical treatments that you think are unlikely to work because they are not scientific. ADJ: ADJ n c darkgreen]disapproval 3. When a duck quacks, it makes the noise that ducks typically make. There were ducks quacking on the lawn. VERB: V • Quack is also a noun. Suddenly he heard a quack. N-COUNT; SOUND