'anti-fundamentalist' is built from the prefix 'anti-' (from Greek 'anti-' meaning 'against') plus the noun 'fundamentalist'. 'Fundamentalist' itself comes from 'fundamental' with the agentive suffix '-ist.'

'anti-' derives from Greek 'anti-' meaning 'against'; 'fundamental' comes from Latin 'fundamentum' meaning 'foundation'; 'fundamental' produced the noun 'fundamentalist' in early 20th century (in contexts of religious movements), and 'anti-fundamentalist' formed later by combining 'anti-' with 'fundamentalist' to denote opposition to such movements.

Initially the elements referred separately to 'against' and 'foundation'; over time the combined term came to mean specifically 'opposed to religious or ideological fundamentalism' and is used both as a noun for people and an adjective for attitudes or positions.