turnkey (adj.)

1650s, "jailer," from turn (v.) + key (n.). In reference to a job that only has to be done only once, it is recorded from 1934. The notion probably is of something that can be accomplished with a single turn of a key.

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Definitions of turnkey from WordNet

turnkey (n.)
someone who guards prisoners;
Synonyms: prison guard / jailer / jailor / gaoler / screw