'anti-religion' is formed from the prefix 'anti-' (from Greek 'anti', meaning 'against') + the noun 'religion' (from Latin 'religio').

'religion' came into English via Old French and Latin: Latin 'religio' entered Old French as 'religion' and Middle English adapted it as 'religiun'/'religion'; the prefix 'anti-' (Greek 'anti') was adopted into English formations, and the compound 'anti-religion' arose in Modern English to denote opposition to religion.

Initially formed to mean simply 'against religion,' the term has been used since the 19th/20th centuries to describe ideological, political, or social opposition to religion; its core sense ('opposed to religion') has remained stable though applications have broadened.