'anti-Roman' originates from the prefix 'anti-' (from Greek 'anti' meaning 'against') combined with 'Roman' (from Latin 'Romanus' meaning 'of Rome').

'Roman' comes from Latin 'Romanus', passed into Old French as 'romain' and into Middle English as 'Roman', and the combining prefix 'anti-' (from Greek via Latin/Old French) formed the compound 'anti-Roman' in Modern English.

Initially 'Roman' meant 'of Rome' and 'anti-Roman' meant broadly 'against Rome or Romans'; over time the term also acquired the narrower religious sense 'opposed to the Roman Catholic Church' in certain contexts.