1. a person who sleeps
2. a railroad car with beds for passengers to sleep in
3. something that achieves unexpected success after initially receiving little attention
Usage: informal

Examples

• The baby is a heavy sleeper and rarely wakes up during the night.
• We booked a sleeper train from New York to Chicago.
• The low-budget film turned out to be a sleeper hit at the box office.
• The carpenter installed sleepers to support the new floor.
• Intelligence agencies worry about sleeper agents in foreign countries.
• She’s such a light sleeper that any noise wakes her up.
• The sleeper was more comfortable than flying overnight.