'lactase-inhibiting' originates from modern scientific English as a compound of 'lactase' + the present-participle form 'inhibiting', used to describe an agent that inhibits lactase activity.

'lactase' comes from Latin 'lac, lactis' meaning 'milk' combined with the enzyme-forming suffix '-ase' (coined in biochemical nomenclature in the late 19th century from earlier words like 'diastase'); 'inhibiting' derives from Latin 'inhibēre' (via Late Latin/Old French), from 'in-' (in/into/against) + 'habēre' (to hold). These elements were joined in modern English scientific usage to form the compound adjective.

Individually, 'lactase' originally denoted 'milk' (root) with '-ase' indicating an enzyme, and 'inhibit' originally meant 'to hold back or restrain'; together in modern usage they specifically denote 'blocking or reducing the enzyme lactase's activity'.