'women-only' originates from Modern English, specifically a compound of 'women' and 'only', where 'women' ultimately derives from Old English 'wīfmann' (with 'wīf' meaning 'woman' and 'mann' meaning 'person') and 'only' comes from Old English 'anlic' where 'an' meant 'one'.

'woman' changed from Old English 'wīfmann' to Middle English forms such as 'wymmen' and eventually became the modern English word 'woman'; 'only' evolved from Old English 'anlic' to Middle English 'onliche' and then to modern 'only'. The compound 'women-only' formed in modern usage as a fixed adjective phrase.

Initially the parts meant 'woman/person' and 'one/sole', and over time the compound came to mean 'restricted exclusively to women' as a fixed adjective phrase.