The Collaborative International Dictionary of English v.0.48:
Extremist \Ex*trem"ist\, n. A supporter of extreme doctrines or practice; one who holds extreme opinions. [1913 Webster]WordNet (r) 3.0 (2006):
extremist adj 1: (used of opinions and actions) far beyond the norm; "extremist political views"; "radical opinions on education"; "an ultra conservative" [syn: extremist, radical, ultra] n 1: a person who holds extreme views