The noun 'turnoff' is a modern compound formed from the phrasal verb 'to turn off'. The verb 'turn' has a long history, tracing back to the Latin tornare, meaning to shape on a lathe, which evolved into the general sense of changing direction. The particle 'off', of Germanic origin, signifies separation or moving away. When combined, the literal action of 'turning off' a road gave rise to the first concrete meaning for a side road. Through metaphorical extension, this sense of diverting from a path was applied to abstract concepts, leading to the second meaning: something that diverts or diminishes one's interest or arousal, effectively causing a person to 'turn away' from it.

Structure: turn (to rotate, to change direction) + off (away, from) - turn: From Old English turnian (to turn, rotate), from Latin tornare (to turn on a lathe). In this compound, it functions as a verb indicating a change in direction or state. - off: From Old English of (away, from). In this compound, it functions as an adverbial particle indicating separation, cessation, or departure.