2. An individual who pretends to be a medical doctor; someone whose medical practice is suspect or not authorized; a charlatan: Mildred always joked that she was going to see her quack about her arthritis.
That quack almost killed Marvin's brother by prescribing the wrong medication.
The quack doctor had a signature laugh which sounded just like the quack of a duck.
2. A charlatan, a phony or a fake: Dana realized that the psychiatrist was really a quack and so she decided to go to the clinic for help.
3. Etymology: a quack or "fake doctor", is a short form of quacksalver, from Dutch kwakzalver, "charlatan".
Dutch kwakken means "to quack", so the word may originally have meant "someone who quacks boastfully, like a duck, about his salve or other medical remedies".