Mennonist \Men"non*ist\, Mennonite \Men"non*ite\, n. (Eccl. Hist.) One of a small denomination of Christians, so called from Menno Simons of Friesland, their founder. They believe that the New Testament is the only rule of faith, that there is no original sin, that infants should not be baptized, and that Christians ought not to take oath, hold office, or render military service.