'milk-inhibiting' is a modern English compound combining 'milk' (from Old English 'milc'/'meolc') and 'inhibit' (from Latin 'inhibēre'), where 'in-' meant 'in/on/into' (later forming a negating sense with some verbs) and 'hibēre' meant 'to hold back'.

'milk' comes from Old English 'milc/meolc' and has been used in Germanic languages for the substance produced by mammals; 'inhibit' comes from Latin 'inhibēre' (via late Latin/Old French influences) meaning 'to hold back' and entered English in post-medieval usage; the compound 'milk-inhibiting' is a transparent modern formation used in medical/clinical contexts to describe agents or actions that inhibit milk production.

The component 'inhibit' originally meant 'to hold back' in Latin and retained that core meaning in English; combined with 'milk' the compound came to mean specifically 'holding back milk production' in modern medical usage.