Turnkey
Bouvier's Law Dictionary and Concise Encyclopedia · John Bouvier; revised by Francis Rawle · 1914
Bouvier's Law Dictionary and Concise Encyclopedia
A person under the superintendence of a jailor, whose employment is to open and fasten the prison-doors and to prevent the prisoners from escaping. It is his duty to use due diligence; and he may be punished for gross neglect or wilful misconduct in permitting prisoners to escape.