'chair-back' is a compound formed from 'chair' and 'back'. 'chair' originates from Old French, specifically the word 'chaiere' (from Latin 'cathedra') where 'chaiere' meant 'seat'; 'back' originates from Old English, specifically the word 'bæc', where 'bæc' meant 'back'.

'chair' passed into Middle English from Old French 'chaiere' (Latin 'cathedra'), and 'back' comes from Old English 'bæc'; these words were later combined in Modern English to form the compound 'chair-back'.

Initially, the parts referred separately to a 'seat' ('chair') and a 'rear surface' ('back'); over time the compound came to be used specifically for the 'back part of a chair'.