'fideist' originates from Latin, specifically the word 'fides', where 'fides' meant 'faith', combined with the agent-forming suffix '-ist' (from Greek/Latin suffixes meaning 'one who').

'fideist' developed from the noun 'fideism' (from Latin 'fides' + '-ism') with the addition of '-ist' to denote an adherent; the -ism form appeared in scholarly and theological use in the 18th–19th centuries and '-ist' produced 'fideist' as the term for a follower.

Initially related simply to matters of 'faith' ('fides'), the term evolved to denote specifically someone who holds the philosophical view that faith is independent of or superior to reason.