Sleeper \Sleep"er\, n. 1. One who sleeps; a slumberer; hence, a drone, or lazy person. [1913 Webster] 2. That which lies dormant, as a law. [Obs.] --Bacon. [1913 Webster] 3. A sleeping car. [Colloq. U.S.] [1913 Webster] 4. (Zool.) An animal that hibernates, as the bear. [1913 Webster] 5. (Zool.) (a) A large fresh-water gobioid fish ({Eleotris dormatrix}). (b) A nurse shark. See under {Nurse}. [1913 Webster]