Other forms: sleepers
A sleeper is a person who is asleep, and the word nearly always comes with a description in front of it: a heavy sleeper who slept through the storm, a light sleeper woken by the cat on the stairs. From there English sends it off to do three or four other jobs entirely.
On the railway, sleepers are the wooden or concrete beams laid across the ground under the rails to hold them apart; Americans call the same beam a tie. A sleeper is also the overnight train or the carriage with beds in it — take the sleeper to Inverness. In spying, a sleeper is an agent planted years in advance and left to live an ordinary life until somebody activates them, which is where sleeper cell comes from. In film and music it is the quiet release that becomes a hit months later, when nobody was watching. All of them share one picture: something lying still, waiting.
1nounasleepA person who is asleep, especially thought of by how easily they wake.
“He is such a heavy sleeper that the fire alarm barely reached him.”
2nounrailA beam laid across the ground beneath railway rails to hold them in place.
“The old sleepers were pulled up and sold for garden walls.”
synonyms: tie
3nountrainA train or railway carriage with beds for overnight travel.
“They booked a sleeper from Paris to Venice.”
4nounsleeperA spy placed somewhere long in advance who stays inactive until needed.
“The trial exposed a sleeper who had run a hardware shop for twenty years.”
5nounbecomesSomething that becomes a success long after it appears, without anyone expecting it.
“The film was a sleeper, ignored in March and sold out by August.”
Sleeper is Middle English sleper, which is sleep with -er on the end and nothing else. Everything the word does now grew out of that plainness: the beam lies still under the track, the agent lies still inside an ordinary life, the film lies still on the shelf until someone notices it. English rarely gets this much work out of so little.
Middle English
sleper
English, today
sleeper
From Middle English sleper, equivalent to sleep + -er.
Etymology from Wiktionary, CC BY-SA