'gay-themed' originates from modern English as a compound of 'gay' and 'themed' (from 'theme'). 'gay' ultimately comes from Old French 'gai' (from a Germanic source) where 'gai' meant 'joyful', and 'theme' comes from Greek 'thema' via Latin and Old French, where 'thema' meant 'something set or placed'.

'gay' changed from Old French 'gai' into Middle English 'gay' and originally meant 'joyful' or 'carefree'; in the 20th century it shifted to denote 'homosexual'. 'theme' passed from Greek 'thema' to Latin and Old French 'theme' before entering Middle/Modern English. The compound 'gay-themed' arose in late 20th-century English to describe works or events with gay subject matter.

Initially, 'gay' meant 'joyful' (or 'carefree'), but over time it evolved to mean 'homosexual'; consequently 'gay-themed' came to mean 'about or featuring homosexuality' rather than anything related to joyfulness.