Excerpt from Chesterfield County, Virginia Wills, 1774-1795.
quack2
n
1.
a. an unqualified person who claims medical knowledge or other skills
b. (as modifier) a quack doctor
2. (Medicine) Brit, Austral, and NZ informal a doctor; physician or surgeon
vb (intr) to act in the manner of a quack
[short for quacksalver]