- a person who sleeps in a particular way
- a light sleeper [=someone who does not sleep well and wakes up easily]
- a heavy sleeper [=someone who sleeps well and does not wake up easily]
- a sound sleeper
- Sleepers were awakened by the sound of a loud crash.
- the sleeper cab of a truck
- Our guests will use the sleeper sofa. [=a sofa that folds out to form a bed]
- someone or something that suddenly becomes successful in a way that was not expected
- He may turn out to be the sleeper in this year's election.
- The movie was the summer's sleeper.
- The movie became the sleeper hit of the summer.
- a sleeper agent
- The police discovered a sleeper cell [=a small organized group of spies] that had been operating in the city for years.