'antireformer' originates from Modern English, formed from the prefix 'anti-' (from Greek 'anti' meaning 'against') and the noun 'reformer' (from 'reform' + agent suffix '-er').

'anti-' comes from Greek 'anti' and entered English as a productive prefix via Latin/French; 'reform' comes from Latin 'reformare' through Old French 'reformer' and Middle English 'reformen', which produced the agent noun 'reformer' and later the compound 'antireformer' in Modern English.

Initially it combined the elements meaning 'against' + 'one who reforms'; over time it has been used straightforwardly to mean 'a person opposed to reforms' with little change in core sense.