A warder or jailer/gaoler; keeper of the keys in a prison.
"The old turnkey knew every hidden tunnel and secret passage within the castle walls better than the king himself."
To supply a turnkey product; to supply something fully assembled and ready to use.
"The construction firm offered us a turnkey solution for our new factory, delivering the building complete with all machinery installed and operational by Monday morning."
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)
"The company decided to invest in a turnkey solar farm that required no additional setup before immediately generating power."