Definition: a religious fanatic
Berndt Knipperdolling was a prominent Anabaptist (a member of a sect of 16th century Protestants who advocated the baptism and church membership of adult believers only), born in Munich at the end of the 15th century. Knipperdolling’s religious views were not shared by some authorities, and he came to an untimely end as a result of them. While initially knipperdolling was simply used as a term for an Anabaptist, it came to later take on the connotation of religious fanaticism.
…there starts up another kind of Government, hatch'd by a Committee of Safety; (of slavery, they meant) who were a rude rabble of Factious, Illiterate, Phanatick, Disloyal Rebels; a knot of Knipperdolings; of the same stamp with that German Botcher, Jack-a-Leyden: the very merdaille and excrementitious offscouring of the Nation.
—J. G. (gent.), The Sage Senator Delineated, 1660
(Source: Merriam-Webster Online "10 polite words for impolite people")