'hairpiece' originates from English, specifically a compound of the words 'hair' and 'piece'. 'hair' goes back to Old English 'hær' meaning 'hair', and 'piece' comes via Old French 'piece' (from Late Latin 'petia') meaning 'a part or fragment'.

'hairpiece' developed in Modern English from the descriptive phrase 'hair piece' (literally 'a piece of hair') and became established as a single compound word as its use specialized to mean a small wig or artificial hair item.

Initially it could be understood as literally 'a piece of hair', but over time it came to mean specifically 'a small wig or artificial hair made to cover or decorate', the current common sense.