Lewis & Short

carcĕrārĭus, a, um, adj. [carcer], 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.