'antifundamentalist' originates from English, specifically as a compound of the prefix 'anti-' meaning 'against' and the noun 'fundamentalist' meaning 'one who adheres to fundamentalism'.

'fundamentalist' itself comes from 'fundamental' + '-ist'; 'fundamental' originates from Latin 'fundamentum' meaning 'foundation'. The modern English term 'fundamentalist' arose in the early 20th century (from the theological movement called Fundamentalism), and 'anti-' has been prefixed to it in later 20th-century usage to form 'antifundamentalist' (or 'anti-fundamentalist').

Initially, 'fundamentalist' referred specifically to a member of the early 20th-century Protestant movement defending core doctrines; over time it broadened to mean someone with strict, literalist adherence to any set of basic principles, and 'antifundamentalist' came to mean someone opposed to such strict adherence.