Word family noun sleep sleeper sleepiness sleeplessness adjective asleep sleepless sleepy verb sleep adverb sleepily sleeplessly
From Longman Dictionary of Contemporary Englishsleepersleep‧er /ˈsliːpə $ -ər/ noun [countable] 1 someone who sleeps in a particular waylight sleeper (=someone who wakes easily)heavy sleeper (=someone who does not wake easily)2 someone who is asleep3 
British EnglishTTT a heavy piece of wood or concrete that supports a railway track SYN tie American English4 TTT a) a night train with carriages that have beds for passengers to sleep in b) a sleeping car c) American English a bed on a train for a passenger to sleep in5 especially American English a film, book etc which is successful, even though people did not expect it to be 6 American English a piece of clothing for a baby that covers its whole body including its feet7 a spy who is sent to a particular place and who lives an ordinary life there until a later time, when they begin their spying activitiesExamples from the Corpus
sleeper• She's good at that too, an accomplished sleeper, with childish face.• People who say they are disturbed by noise at night may just happen to be light sleepers.• Many sleepers are disturbed by light that pervades their eyelids when they have their eyes closed.• Often what is perceived as insomnia by an older sleeper is only a change in sleep length and sleep quality.• He's a restless sleeper, kicking and thrashing about throughout the night.• He had booked on tomorrow night's sleeper, and would head up to Oban on Friday.• The air exerts pressure on the airway, holding it open and allowing the sleeper to breathe normally.heavy sleeper• Or else she had become a heavy sleeper over the years.• Mrs Fairfax is a heavy sleeper, like most old people, and didn't hear anything.• Some people who sleep next to snorers are able to tune out the sound, if they are heavy sleepers.From Longman Business Dictionarysleepersleep‧er /ˈsliːpə-ər/ noun [countable] American EnglishFINANCEMARKETING a share or a product that is not successful immediately, but then suddenly starts to sell well or be successfulThe movie turned out to be a sleeper. 