'turn-on' originates from Modern English as a compound formed by the verb 'turn' + the adverb/preposition 'on', created by nominalizing the phrasal verb 'turn on' (20th century usage for both literal activation and colloquial senses).

'turn' comes from Old French 'torner'/'tourner' (to turn) ultimately from Latin 'tornare' (to turn on a lathe), while 'on' comes from Old English 'on' (in, on). The phrasal combination 'turn on' developed in Middle to Modern English and the hyphenated noun 'turn-on' arose later to name the result or stimulus of that action.

Initially the components conveyed literal sense 'cause to turn' or 'put into motion'; over time 'turn on' broadened to mean 'activate' and, by metaphorical extension in the 20th century, 'cause sexual arousal' or 'excite interest'.