'ill-tempered' originates from English, formed by combining the adjective 'ill' (Old English 'yfel' meaning 'bad') and the noun 'temper' (from Latin 'temperare' via Old French, meaning 'to mix, regulate' and later 'disposition').

'ill' (Old English 'yfel') + 'temper' (Late Latin 'temperare' → Old French 'temperer' → Middle English 'temper') combined in Early Modern English to form the compound adjective 'ill-tempered'.

Initially built from elements meaning 'bad' + 'temper/disposition'; it has long meant 'having a bad disposition' and has retained that basic sense into modern usage.