'outbuilding' is a compound formed from the English element 'out' (originating from Old English 'ūt', meaning 'out' or 'outside') and 'building' (from the verb 'build', Old English related forms meaning 'to construct').

'outbuilding' developed in Middle English as a compound of 'out' + the present-participle/noun form 'building' (literally 'a building outside'), eventually stabilizing as the modern English noun 'outbuilding'.

Initially it referred specifically to any building located outside the main dwelling; over time the meaning has remained largely the same, generally referring to secondary structures on the same property.