Origin of the Term "Quack"

From more than three centuries, unqualified doctors have been known as "quacks". The word is an abreviation of "quacksalver", which meant someone who stood in the street selling salves, or curing potions (he quack part comes from the old Dutch word, "quacken", meaning to boast or cry out).
The hawkers may have boasted about the miraculous properties of their cures, but whatever they sold was more likely to make things worse rather than curing the sick. So the term quickly came to mean a medical charlatan.