n. A bridge-tower, gate-tower, outlying defense, or citadel.n. In French history, a fortress used as a state prison.n. Hence By extension, any prison, especially one conducted in an arbitrary or oppressive way.n. A movable tower used by the besiegers of a strong place, whether for approaching the walls (see belfry) or as a defense and protection for the besiegers.To confine in a bastile; imprison.