'chymosin' originates from modern scientific coinage derived from Greek 'khymos' (χυμός) meaning 'juice' or 'fluid', combined with the enzyme-forming suffix '-in'.

'Chymosin' replaced the older/common term 'rennin' (from rennin/rennet usage) as biochemical nomenclature developed; the name reflects formation from Greek roots rather than the folk term 'rennet'.

Initially used to denote the active milk-coagulating principle in animal rennet, its modern use refers more specifically to the identified aspartic protease enzyme (including recombinant forms) with that activity.