'different-sex' is a modern English compound formed from 'different' and 'sex'. 'different' ultimately originates from Latin, specifically the word 'differens', where the prefix/root 'dis-' (or 'dif-') meant 'apart' and 'ferre' meant 'to carry'; 'sex' originates from Latin 'sexus', meaning 'gender' or 'sex'.

'different' came into English via Old French/Middle English from Latin 'differens' (present participle of 'differre'), while 'sex' came into English from Latin 'sexus' (via Old French into Middle English); the two English words were later combined as a compound adjective 'different-sex' in modern English usage.

Individually, 'different' initially meant 'not the same' and 'sex' referred to biological category; when combined as 'different-sex' the compound specifically conveys 'involving persons of different sexes' (i.e., opposite-sex).