sleeper

sleeper — noun

1. someone whose rest is described by qualities such as how deeply they sleep or ho

1.nounA2
Definition

someone whose rest is described by qualities such as how deeply they sleep or how easily they are woken

Example

Sumin is such a light sleeper that even a soft cough wakes her up.

collocation: light sleeper / heavy sleeper

Tuan is a heavy sleeper who never stirs during a thunderstorm.

Common collocations
  • light sleeper
  • heavy sleeper
  • sound sleeper
  • deep sleeper

Grammar Patterns

adjective + sleeper

Usage Note

Adjectives commonly used before 'sleeper' include 'light', 'heavy', 'deep', 'sound'. This sense does not describe a physical position or location of sleeping.

Common Mistakes

I am a light sleeper person.
I am a light sleeper.
'sleeper' already means a person; do not add 'person' after it.

2. a railway coach fitted with berths where travellers can rest overnight, or the b

2.nounB1
Definition

a railway coach fitted with berths where travellers can rest overnight, or the berth itself, or the train providing this accommodation

Example

The overnight train from Taipei to Taitung has a comfortable sleeper carriage.

sleeper carriage

Adisa booked a bed in a sleeper for the long journey across France.

book + a bed in a sleeper

Common collocations
  • sleeper train
  • sleeper carriage
  • sleeper compartment
  • book a sleeper
Synonyms
  • sleeping car

    more formal or technical term for a railway carriage with beds

  • couchette

    a cheaper, simpler type of train bed often in an open compartment

Usage Note

Can refer to the carriage ('a sleeper'), the bed ('a berth in a sleeper'), or the whole train ('a sleeper train'). Common in travel contexts.

Common Mistakes

I slept in a sleeper bed.
I slept in a sleeper.
'sleeper' already includes the bed; 'sleeper bed' is redundant.

3. a strong horizontal block placed under the rails of a railway to hold them in po

3.nounB2
Definition

a strong horizontal block placed under the rails of a railway to hold them in position, typically fashioned from timber or cement

Example

The railway workers replaced the old wooden sleepers with concrete ones.

wooden sleepers / concrete sleepers

A rotten sleeper can make the track uneven and cause trains to shake.

Common collocations
  • wooden sleeper
  • concrete sleeper
  • replace a sleeper
  • railway sleeper
Synonyms
  • railroad tie

    the standard American English term for the same object

Usage Note

Called 'railroad tie' in American English. In Taiwan, 枕木 is the common term, though modern sleepers are often concrete rather than wood.

4. a small ring or stud, often gold or silver, that is inserted into a pierced ear

4.nounB1
Definition

a small ring or stud, often gold or silver, that is inserted into a pierced ear to keep the earlobe opening from healing shut when no other jewellery is being worn

Example

Caleb wears a small gold sleeper in his left ear to keep the hole open.

gold sleeper / silver sleeper

After the party, Jessica took out her dangling earrings and put in sleepers.

Common collocations
  • gold sleeper
  • silver sleeper
  • pair of sleepers
  • put in a sleeper
  • wear a sleeper
Synonyms
  • stud

    a small earring that sits on the earlobe without hanging, but not specifically for keeping a piercing open

Usage Note

Usually worn when the wearer does not want a visible or dangling earring — for example at night, at work, or during sports. Sold in pairs.

Common Mistakes

I bought a sleeper earring.
I bought a sleeper.
'sleeper' alone is sufficient and more natural; 'sleeper earring' is redundant.

5. a person, film, book, or product that gains sudden and surprising popularity fol

5.nounB2
Definition

a person, film, book, or product that gains sudden and surprising popularity following an extended stretch of going largely unnoticed or underappreciated

Example

The low-budget film was a sleeper that nobody expected to make money.

sleeper hit / sleeper success

Layla's first novel was a sleeper that only became famous two years after its release.

sleeper + become famous / become popular

Common collocations
  • sleeper hit
  • sleeper success
  • be a sleeper
Synonyms
  • dark horse

    used more often for a person than a product, especially in sports or competitions

  • surprise hit

    more direct and less idiomatic than 'sleeper hit'

Antonyms
  • flop

    a product that fails despite expectations

Grammar Patterns

a sleeper + hit / success / film

Usage Note

Commonly used with 'hit' — 'sleeper hit' is a fixed phrase. Also used in sports for a team or player who performs much better than expected.

Common Mistakes

The movie was a sleeper hit success.
The movie was a sleeper hit.
'hit' already means success; adding 'success' is redundant.

6. an intelligence agent placed in a foreign country or organization who lives as a

6.nounC1
Definition

an intelligence agent placed in a foreign country or organization who lives as an ordinary citizen and remains inactive until directed to carry out an operation

Example

The intelligence agency had placed a sleeper in the capital years before the operation.

place a sleeper

A sleeper may live a normal family life for a decade before receiving orders.

Common collocations
  • sleeping agent
  • place a sleeper
  • activate a sleeper
  • sleeper cell
Synonyms
  • mole

    a spy who works inside an organization gathering information, not necessarily dormant

  • asset

    a broader term for any spy or informant used by an intelligence service

Usage Note

Distinguish from 'mole' — a mole works inside an organization and actively gathers information, while a sleeper remains dormant until activated.

7. a full-length infant garment that wraps the baby from the neck down to the toes,

7.nounB1
Definition

a full-length infant garment that wraps the baby from the neck down to the toes, typically made of soft fabric and worn as nighttime clothing

Example

Noa dressed the baby in a warm fleece sleeper before putting him in the cot.

dress + baby + in a sleeper

The cotton sleeper has buttons from the neck down to the toes for easy changes.

Common collocations
  • baby sleeper
  • cotton sleeper
  • fleece sleeper
  • warm sleeper
  • newborn sleeper
Synonyms
  • sleepsuit

    the common British English term for the same garment

  • babygro

    a brand name often used generically in the UK for baby sleepers

  • footed pajama

    the American English term

Usage Note

Also called a 'sleepsuit' or 'babygro' in British English. In American English it may be called a 'footed pajama'. Usually made of soft cotton or fleece and often has a zip or snap buttons.

Word family

Synonym discussion

Sense: noun/5

All four words describe something that achieves unexpected success, but they differ in scope and connotation. A 'sleeper' specifically implies a long period of obscurity before a sudden breakthrough; it is commonly used for films, books, and products (e.g., 'that indie film was a sleeper'). A 'dark horse' is a competitor or candidate who was not expected to win but does — it is more common in sports and politics. A 'surprise hit' is a straightforward, less idiomatic term for any unexpectedly popular work. An 'underdog' is a person or team thought unlikely to succeed, often because of a disadvantage (less money, less experience); the focus is on the struggle against odds rather than on sudden fame. Example: 'The small bakery was a sleeper — no food critics reviewed it for two years. Then a single post on social media turned it into a surprise hit, proving that every underdog has a chance.'

sleeper ↗dark horsesurprise hitunderdog ↗

Etymology

Old EnglishMiddle EnglishEnglish

The word 'sleeper' comes from the Old English word 'slǣpan' (to sleep), combined with the suffix '-er' meaning a person or thing that does something. The core meaning — 'one who sleeps' — dates back to the early 1200s. Over the centuries the word branched out: in the 1830s, railways adopted 'sleeper' for the horizontal beams that 'sleep' under the rails, supporting the track. The train-carriage meaning appeared in the 1870s as train travel became popular. The 'spy' sense emerged during the Cold War, describing an agent who 'sleeps' or lies dormant until needed. The 'unexpected success' meaning grew from horse-racing slang in the mid-1900s, where a horse that performed far better than expected was called a 'sleeper'. The 'baby garment' and 'earring' meanings both developed in the 20th century, each describing something that stays in place or is worn while sleeping.