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• reef
  reef

  noun

  a ridge of rocks or sand, often of coral debris, at or near the surface of the water.
• Reef
  Reef

  noun

  another name for the Great Barrier Reef

reef

¹ American  

[reef] / rif /

noun

1. a ridge of rocks or sand, often of coral debris, at or near the surface of the water.

2. Mining. a lode or vein.

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reef ² American  

[reef] / rif /

noun

1. a part of a sail that is rolled and tied down to reduce the area exposed to the wind.

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verb (used with object)

1. to shorten (sail) by tying in one or more reefs.

2. to reduce the length of (a topmast, a bowsprit, etc.), as by lowering, sliding inboard, or the like.

3. to pull (old oakum) out of seams, as with a rave hook (often followed byout ).

reef ¹ British  

/ riːf /

noun

1. a ridge of rock, sand, coral, etc, the top of which lies close to the surface of the sea

2. a ridge- or mound-like structure built by sedentary calcareous organisms (esp corals) and consisting mainly of their remains

3. a vein of ore, esp one of gold-bearing quartz

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Reef ² British  

/ riːf /

noun

1. another name for the Great Barrier Reef

2. another name for the Witwatersrand

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reef ³ British  

/ riːf /

noun

1. the part gathered in when sail area is reduced, as in a high wind

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verb

1. to reduce the area of (sail) by taking in a reef

2. (tr) to shorten or bring inboard (a spar)

reef Scientific  

/ rēf /

1. A strip or ridge of rocks, sand, or coral that rises to or near the surface of a body of water.

2. See more at coral reef

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Other Word Forms

• unreefed
  adjective

Etymology

Origin of reef¹

1575–85; earlier riff ( e ) < Dutch rif

Origin of reef²

1350–1400; Middle English refe (noun) < Dutch reef

Explanation

A reef is a raised area on the ocean floor that's made of rock, coral, or sand. If you are a scuba diver, head to a coral reef to check out the diverse marine life. A barrier reef is one that surrounds an island and creates a lagoon between the reef and the beach. When this type of reef attracts diverse ocean life, it can be popular with snorkelers and scuba divers. When you're sailing, a reef is a section of the sail that you can roll up when necessary — and to reef is to roll up a reef. Both meanings share an Old Norse root, rif, "ridge under the water."

Example Sentences

The team combined satellite measurements of ocean surface temperatures from the Coral Reef Watch system with on site reef surveys and aerial observations collected worldwide.

From Science Daily • Feb. 12, 2026

Australia's Great Barrier Reef, for instance, saw peak heat stress increase each year between 2014 and 2017.

From Barron's • Feb. 10, 2026

I first met Andrews at her downtown studio on the top floor of the Reef building in South L.A. a few days after the anniversary of the Palisades fire.

From Los Angeles Times • Jan. 27, 2026

At Western Australia’s Sal Salis Ningaloo Reef, set beside the Indian Ocean’s aquamarine waters, the nightly rate starts at around $520 per person.

From The Wall Street Journal • Dec. 10, 2025

There was another thing I needed to travel to Queensland, Australia, at the edge of the Great Barrier Reef.

From "The Thing About Jellyfish" by Ali Benjamin

Related Words

• atoll
• beach
• coral reef
• shoal