Penitentiary meaning : A state or federal prison for convicted felons; (broadly) a prison. A priest in the Roman Catholic Church who administers the sacrament of penance. One who prescribes the rules and measures of penance. One who does penance. A small building in a monastery, or a part of a church, where penitents confessed. An office of the papal court which examines cases of conscience, confession, absolution from vows, etc., and delivers decisions, dispensations, etc.; run by a cardinal called the Grand Penitentiary who is appointed by the pope. An officer in some dioceses since 1215, vested with power from the bishop to absolve in cases reserved to him. Of or relating to penance; penitential. Of or relating to the punishment of criminals.