- 1(used with an adjective) a person who sleeps in a particular way a heavy/light/sound sleeper
- 2a person who is asleep Only the snores of the sleepers broke the silence of the house.
- 3 a night train with beds for passengers on it the Washington, D.C. to Los Angeles sleeper I came up last night on the sleeper.
- 4 = sleeping car
- 5 (informal) a movie, play, or book that for a long time is not very successful and then is suddenly a success
- 6 (also sleeper agent) a spy who is sent to live in a country as a normal citizen and is not used until much later The sleeper had lived in the U.S. for two decades. He infiltrated a terrorist sleeper cell.