Known in our language for some four hundred years, the term “Quacksalver” nevertheless was soon felt to be unmanageably long and was reduced to quack, with which we are more familiar today.
The quacksalver was originally an unscrupulous or false physician, one who quacked (hawked, or bragged of) his salves (ointments).
Today, the quack is any charlatan, though still often a make-believe or unethical medical doctor.
The word is supposed to have come to us from the Dutch, but the ultimate origin is in considerable doubt, as the same term, with suitable modifications in spelling, is known widely throughout the Germanic languages.