'rennet' originates from Middle English, specifically the word 'rennet', where it referred to the stomach or its lining used to curdle milk.

'rennet' changed from Middle English 'rennet' (used for the animal stomach product) and eventually became the modern English word 'rennet' referring more broadly to the enzyme preparation.

Initially, it meant 'the stomach or stomach lining of a young ruminant used to curdle milk', but over time it evolved into its current meaning of 'an enzyme preparation used to coagulate milk'.