'sex-related' originates from modern English, specifically the compound of 'sex' and 'related', where 'sex' comes from Latin 'sexus' meaning 'state of being male or female' and 'related' comes from Latin 'relatus' (past participle of 'referre') meaning 'brought back' or 'connected'.

'sex' changed from Latin 'sexus' to Old French 'sexe' and then to Middle English 'sex'; 'related' developed from Latin 'referre' -> past participle 'relatus' through Old French/Medieval Latin into Middle English 'related'. The compound 'sex-related' formed in modern English by combining the two words to describe things connected to sex.

Initially, 'sex' primarily meant 'the state of being male or female'; over time its sense broadened to include sexual activity and sexuality more generally. Accordingly, 'sex-related' originally referred mainly to biological sex differences but now commonly covers sexual behavior, health, and other issues connected to sexuality.