noun

sleeper

SLEE-puh

noun

Someone who is sleeping.

"She's a light sleeper — the slightest noise wakes her up."

A spy or agent who lives an ordinary life in a community until activated for a mission.

"The film follows a Cold War sleeper waiting years for a single coded message."

Something — a film, product, or competitor — that unexpectedly becomes a big success after being overlooked.

"The low-budget film became a sleeper hit, earning ten times its budget."

(British) A wooden or concrete beam laid under railway tracks to support them; a railroad tie.

"Workers replaced the rotting sleepers along that stretch of track."

A car that has been heavily modified for performance while still looking ordinary.

"His beat-up sedan was a total sleeper — it could outrun most sports cars off the line."

How to Use Sleeper

Learner’s notes

In plain EnglishSomeone or something asleep, dormant, or hidden — until it unexpectedly succeeds or gets activated.

UK vs US

"Sleeper" for a railroad tie is standard British usage; American English calls the same thing a "tie."

Common pairings

sleeper cell sleeper hit railway sleeper

sleepered past tense, sleepers plural, sleepers plural, Sleepers plural, sleepers singular

Study it as flashcards or scroll it in Flow — saved to your collection.

Can you complete this real example?

She's a light _____ — the slightest noise wakes her up.

Formed from "sleep" plus the agent suffix "-er," originally just meaning "one who sleeps."

leper keeper peeper beeper sweeper creeper steeper beekeeper innkeeper zookeeper goalkeeper shopkeeper