the compound "turnkey" originated in the early 17th century, directly from the literal action of a jailer who "turns the key" to lock or unlock a cell. this concrete occupational term leveraged the germanic "key" and the latinate "turn" to denote the person performing this specific duty. by the mid-20th century, the term underwent semantic broadening in commercial and technical contexts, applying the concept of "ready to operate with a simple turn of a key" to systems, projects, or properties supplied in a complete, immediately functional state. this evolution reflects a metaphorical shift from a human agent performing an action to an attribute of a system requiring minimal initial effort from the user.

Structure: turn + key turn (from old english turnian, tyrnan, meaning "to rotate, revolve", of latin origin via old french; functional role: verb root indicating action). key (from old english cǣg, meaning "metal instrument for locking/unlocking"; functional role: noun, the object of the action).