'lactase' originates from New Latin components 'lact-' and the suffix '-ase', where 'lact-' (from Latin 'lac, lactis') meant 'milk' and '-ase' is an enzyme-forming suffix coined in the 19th century.

'lactase' was formed by combining the Latin root 'lac' (milk) with the scientific suffix '-ase' in modern biochemical terminology, producing the term used in contemporary biology and medicine.

Initially, it meant 'an enzyme that acts on lactose (milk sugar)'; over time the meaning has remained largely the same and continues to denote that specific enzymatic activity.