reef

reef — noun

1. A long, narrow band of rock, coral, or sand that sits just beneath the water's s

1.nounB1
Definition

A long, narrow band of rock, coral, or sand that sits just beneath the water's surface, creating a serious danger for ships in the area.

Example

The ship's captain warned the crew to stay clear of the coral reef ahead.

coral reef — common collocation

Soraya saw colourful fish swimming near the reef during her first snorkelling trip.

Common collocations
  • coral reef
  • barrier reef
  • hidden reef
  • reef system
  • reef ecosystem
Synonyms
  • shoal

    a submerged sandbank, less rocky and often visible at low tide

  • sandbar

    a ridge of sand built up by currents, usually in rivers or along coasts

  • atoll

    a ring-shaped coral reef surrounding a lagoon, found in tropical oceans

Antonyms
  • open sea

    deep water without submerged obstacles

Grammar Patterns

a/an + reef

the + reef

adjective + reef

Usage Note

Often used in compound names: 'coral reef', 'barrier reef'. The most famous example is the Great Barrier Reef off the coast of Australia.

Common Mistakes

We swam at the reef' (if meaning a sandy beach).
We swam near the reef.
a reef is a rocky or coral structure, not a sandy shore.

2. A foldable portion of a ship's sail that sailors roll up or tie down to shrink t

2.nounB2
Definition

A foldable portion of a ship's sail that sailors roll up or tie down to shrink the area exposed to strong wind.

Example

Joaquín tied the reef in the mainsail before the storm arrived.

tie the reef — verb + reef collocation (sailing)

The sailors pulled hard on the ropes to take in a reef.

Common collocations
  • take in a reef
  • put in a reef
  • shake out a reef
  • reef points
  • tie the reef

Grammar Patterns

a/an + reef

take in + a reef

put in + a reef

tie + the + reef

Usage Note

Common in nautical expressions: 'take in a reef' means to reduce sail area; 'shake out a reef' means to release the folded section and expand the sail again. The number of reefs taken is counted: 'one reef', 'two reefs'.

3. Something that blocks progress or causes unexpected difficulty, used like a hidd

3.nounC1
Definition

Something that blocks progress or causes unexpected difficulty, used like a hidden rock reef that threatens a ship.

Example

The project hit a reef of unexpected costs that delayed the construction.

'a reef of [problems]' — figurative use

Abigail's plan ran into a reef of legal problems she had not predicted.

Common collocations
  • a reef of problems
  • a reef of difficulties
  • a reef of debt
  • hit a reef
  • strike a reef
  • run into a reef
Synonyms
  • obstacle

    a neutral, non-metaphorical term for something that blocks progress

  • pitfall

    a hidden or unsuspected danger, similar in figurative tone

Antonyms

Grammar Patterns

a reef of + noun (problems, difficulties, issues)

Usage Note

Primarily appears in formal writing and journalism rather than everyday speech. Often paired with verbs like 'hit', 'strike', or 'run into' to maintain the nautical metaphor.

reef — verb

Word family

  • reefed
    adjectiveC1
  • reefing
    nounC1

Synonym discussion

Sense: noun/1

A 'reef' is a submerged ridge of rock, coral, or sand that rises near the surface and poses a danger to ships. 'Shoal' refers to a shallow area, usually of sand or mud, that is often visible at low tide — it emphasises the shallow water more than the hard structure. 'Sandbar' is a ridge of sand built up by currents, typically found at river mouths or along shores, and is less permanent than a coral reef. 'Atoll' is a specific type of ring-shaped coral reef that encloses a lagoon, found only in tropical oceans. 'Cay' (pronounced 'key') is a small, low island formed on top of a coral reef, made of sand or coral debris. For example: the ship avoided the reef, but smaller boats could cross the shoal; the Pacific has many atolls, each with a sandy cay on the reef ring.

reef ↗shoalsandbaratollcay

Common collocations

Phrases

  • take in a reef
  • put in a reef
  • hit a reef
  • strike a reef

Prepositions

  • on a reef
  • over a reef
  • near a reef
  • off the reef

Etymology

Old NorseMiddle Dutch / Middle EnglishEnglish

The word 'reef' comes from Old Norse 'rif', meaning 'rib'. The rock ridge sense developed because a line of rocks looks like the ribs of a body lying under the water. The sailing sense also traces back to the same root — the folded part of a sail was seen as being rib-like. English sailors picked up the word through Dutch and Scandinavian maritime contacts around the 14th–15th centuries.