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