'extremist' originates from the English adjective 'extreme' combined with the agent suffix '-ist', ultimately tracing back to Latin 'extremus', where 'extra' (or the root) meant 'outside' or 'outermost'.

'extreme' came into English via Old French and Middle English from Latin 'extremus'; the noun 'extremist' was formed in modern English by adding the suffix '-ist' to 'extreme'.

Initially related to the idea of being at the outermost or greatest degree ('extreme'); over time the term came to denote a person who holds extreme (often political or religious) views, especially one favoring radical or violent action.