'antirennin' originates from Greek prefix 'anti-' meaning 'against' combined with New Latin/modern scientific formation 'rennin' (from 'rennet'), where 'anti-' meant 'against' and 'rennin' referred to the milk‑coagulating enzyme derived from calf stomach.

'antirennin' developed in modern scientific/medical usage from the combination of 'anti-' + 'rennin'; 'rennin' itself comes from Middle English/Old French 'renet'/'rennet' (referring to the calf stomach or its curdling agent), and this term was adapted into New Latin and modern scientific vocabulary as 'rennin'.

Initially the components literally meant 'against' + 'rennin' (the curdling agent); the term has consistently meant an agent that counteracts or neutralizes rennin (chymosin) in scientific contexts.