'antirennet' originates from Modern English, formed by the prefix 'anti-' (from Greek 'anti-' meaning 'against') + 'rennet' (from Middle English 'rennet', referring to the milk-coagulating substance).

'rennet' was attested in Middle English as 'rennet' (or variants) borrowed from Old French forms referring to the curdling agent; 'antirennet' is a later Modern English formation combining 'anti-' with 'rennet'.

Initially it literally meant 'against rennet' (i.e., opposed to rennet); over time it has been used specifically to mean 'a substance that inhibits the action of rennet' (a rennet inhibitor).