'Extremist' definitions:

Definition of 'extremist'

From: WordNet
adjective
(used of opinions and actions) far beyond the norm; "extremist political views"; "radical opinions on education"; "an ultra conservative" [syn: extremist, radical, ultra]
noun
A person who holds extreme views

Definition of 'Extremist'

From: GCIDE
  • Extremist \Ex*trem"ist\, n. A supporter of extreme doctrines or practice; one who holds extreme opinions. [1913 Webster]