'mixed-gender' originates from Modern English as a compound combining the adjective 'mixed' and the noun 'gender'.

'mixed' comes from the past participle of 'mix', ultimately from Latin 'miscēre' (to mix) via later European use; 'gender' comes into English via Old French 'gendre' from Latin 'genus' meaning 'kind' or 'birth'. The compound 'mixed-gender' developed in modern English usage in the 20th century to describe groups or facilities including both sexes.

Initially, 'gender' (from Latin 'genus') meant 'kind' or 'type'; over time it shifted to refer specifically to sex or social categories of sex, and 'mixed' as a descriptor combined with 'gender' came to mean 'including both sexes' in contemporary usage.