'pain-enhancing' originates from Modern English as a compound of 'pain' + the present participle 'enhancing' (from the verb 'enhance'). 'pain' comes via Old French 'peine' from Latin 'poena', and 'enhance' derives from Old French enhauncer (later enhauncer/enhauncen) ultimately from Germanic/Old French roots for 'raise' or 'make higher.'

'pain' came into Middle English from Old French 'peine' (itself from Latin 'poena'), evolving from meanings related to 'penalty/punishment' to physical suffering; 'enhance' came into English from Old French enhauncer and Middle English enhauncen, later becoming modern English 'enhance' and its participle 'enhancing', which combined with 'pain' to form the compound 'pain-enhancing'.

Initially, Latin 'poena' primarily meant 'penalty' or 'punishment,' and over time the sense shifted toward physical suffering, which is the modern sense of 'pain.' 'Enhance' originally meant 'to raise or make higher (in value, quality, or degree),' and this basic sense has been retained; combined as 'pain-enhancing,' it now means 'increasing the degree or intensity of pain.'