'balldress' is a modern English compound formed from 'ball' and 'dress', where 'ball' referred to a formal social dance and 'dress' meant a garment or attire.

'ball' comes into English via Old French 'bal' (a dance), ultimately from Late Latin 'ballare' meaning 'to dance'; 'dress' comes from Old French (Middle English) 'dresser'/'dresse' meaning 'to arrange' or 'make ready' and developed to mean 'clothing' in Middle English, and these two elements were compounded in modern English to form 'balldress' (also seen as 'ball-dress' or 'ball dress').

Initially, 'ball' referred to the dance/event and 'dress' meant to arrange or prepare (and later clothing); together the compound came to mean a garment specifically worn to a ball.