Mennonite (n.)

member of a German Anabaptist sect, 1560s, from name of Menno Simons (1492-1559), founder of the sect in Friesland and chief exponent of its doctrines (adult baptism, refusal of oaths, civic offices, and support of the state in war), + -ite (1). As an adjective by 1727. Alternative form Mennonist (n.) is attested from 1640s.