plural sleepers
1
a
: 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
b
: someone who is asleep
Sleepers were awakened by the sound of a loud crash.
2
a
: a place or piece of furniture that can be used for sleeping
—usually used before another noun
the sleeper cab of a truck
Our guests will use the sleeper sofa. [=a sofa that folds out to form a bed]
b
3
chiefly US, informal
: 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.
4
: a spy who lives and works for a long time like an ordinary person among the people he or she is spying on
—often used before another noun
a sleeper agent
The police discovered a sleeper cell [=a small organized group of spies] that had been operating in the city for years.
5
US
: a piece of clothing that covers the entire body including usually the feet and that is worn by a baby or small child
6
British
: one of the heavy beams to which the rails of a railway are attached : tie
Cite this Entry
“Sleeper.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/sleeper. Accessed 19 Jun. 2026.
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