Lewis & Short

clausūra or clūsūra, ae, f. [claudo].

  1. * I. (Cf. claustra, I. A.) A lock, bar, bolt, Inscr. Orell. 2510.
  2. II. (Cf. claustra, II. B.) A castle, fort (late Lat.), Cod. Just. 1, 27, 2, § 4; Cassiod. Var. 2, 5.