'ill-assorted' originates from English, combining the prefix 'ill-' (from Old English 'ill' / Proto-Germanic *ubilaz meaning 'bad') and 'assorted' from Old French 'assortir', where 'assortir' meant 'to arrange or suit'.

'assorted' changed from Old French 'assortir' and Middle English forms such as 'assorten' and eventually became the modern English 'assorted'; the negative prefix 'ill-' (Old English 'ill') was later attached to form 'ill-assorted' in later English usage.

Initially it described something 'badly sorted or arranged'; over time it evolved to mean more generally 'badly matched' or 'not in harmony' in composition or appearance.