'anti-rennin' is formed from the prefix 'anti-' (from Greek 'anti' meaning 'against') combined with 'rennin' (the name for the milk‑clotting enzyme chymosin).

'rennin' developed in modern scientific usage from the common term 'rennet' (Old French/Medieval Latin terms for the stomach-derived curdling agent); during the 19th–20th centuries 'rennin' or 'chymosin' became the enzyme name, and compounds such as 'anti-rennin' were created by attaching the prefix 'anti-' in modern English scientific formation.

Originally, related words like 'rennet' referred to the stomach substance used to curdle milk; over time the term 'rennin' came to denote the specific enzyme, and 'anti-rennin' evolved to mean anything that opposes or neutralizes that enzyme.