'armpiece' originates from a combination of Old English and Old French elements: Old English 'earm' and Old French 'piece', where 'earm' meant 'arm' and 'piece' meant 'a portion or part'.

'armpiece' developed as a compound in Middle English from the elements 'arm' (from Old English 'earm') and 'piece' (from Old French 'piece'), and eventually became the Modern English word 'armpiece' used for items associated with the arm.

Initially, it meant 'a piece associated with the arm' in a literal, descriptive sense, but over time it evolved to refer specifically to ornamental or protective items worn on the arm.