Someone who guards prisoners.

synonyms: jailer, jailor, prison guard, screw, turnkey.

Roget 753: keeper, custodian, custos [Lat.], ranger, warder, jailer, gaoler, turnkey, castellan^†, guard; watchdog, watchman; Charley; chokidar^†, durwan^†, hayward^†; sentry, sentinel; watch and ward; concierge, coast guard, guarda costa [Sp.], game keeper.    escort, bodyguard.    protector, governor, duenna [Sp.]; guardian; governess etc. (teacher) 540; nurse, nanny, babysitter, catsitter, dogsitter, bonne [Fr.], ayah^†.    ... show more

Dutch: gevangenbewaarder, cipier
Polish: strażnik więzienny