'sex-atypical' originates from modern English, formed by compounding the noun 'sex' and the adjective 'atypical'.

'atypical' comes from Greek elements 'a-' (not) + 'typikos' (of a type) via Latin and French into English; 'sex' comes from Latin 'sexus' (division into male and female) and entered English through Old French/Latin usage. The compound 'sex-atypical' arose in late 20th-century clinical and social-science literature to describe patterns relative to sex norms.

Initially, 'atypical' meant simply 'not typical'; when combined as 'sex-atypical' it came to mean specifically 'not typical for one's sex' in medical, psychological, and gender-discourse contexts.