carcerarius
From LSJ
carcĕrārĭus: a, um, adj. id.,
I of or belonging to a prison: quaestus, of keeping a prison, Plaut. Capt. 1, 2, 20.—Hence, subst.: carcĕrārĭus, ii, m., a prisonkeeper, jailer, Inscr. Grut. 80, 5; Don. ad Ter. Phorm. 2, 3, 26; cf. carcer, I. C. b.