The compound noun "turn-on" is a modern metaphorical extension of the phrasal verb "to turn on," which emerged in the mid-20th century. Literally, the verb phrase means to activate a device, such as turning on a light, implying the initiation of function or power. The figurative sense, from which the noun derives, applies this logic of activation to human psychology and physiology, suggesting something or someone that "switches on" a state of arousal, excitement, or attraction. This evolution showcases a common pattern where technological or mechanical terminology is borrowed to describe abstract emotional or sexual responses, creating a vivid conceptual link between causing a machine to operate and causing a person to feel stimulated.

Structure: turn (to cause to move) + on (to a position of operation or contact) "Turn" originates from Old English turnian, tyrnan (to turn, rotate), from Latin tornare (to turn on a lathe). In this compound, it functions as a verb base meaning to cause a change in state or condition. "On" originates from Old English on, an (in, into, onto, upon), functioning as an adverbial particle indicating a state of activation, contact, or operation.