Lewis & Short

dormītōrĭus, a, um, adj. [dormio], of or for sleeping (post-Aug.): cubiculum, Plin. Ep. 5, 6, 21: so, membrum, id. ib. 2, 17, 9; and subst., dormitorium, ii, n., a sleeping-room, dormitory, Plin. 30, 6, 17, § 51.