Adjective

1. ready to use without further assembly or test; supplied in a state that is ready to turn on and operate (typically refers to an assembly that is outsourced for manufacture)

   They wanted a turnkey solution for the entire system, but we could only provide the enclosure.

Noun

1. A warder or jailer / goaler; keeper of the keys in a prison
   • 1836, Charles Dickens, The Pickwick papers

     ...they passed through an open door into a lobby, from which a heavy gate, opposite to that by which they had entered, and which was guarded by a stout turnkey with the key in his hand, led at once into the interior of the prison.

Verb

1. to supply a turnkey product; to supply something fully assembled and ready to use

   We can sell you all the parts, or we can turnkey the entire unit.