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 film cuts to a hummingbird sipping nectar from a flower on a cactus, a sea turtle floating over a coral reef, pink flamingos on a green lake, a snowflake, a butterfly.

From The Wall Street Journal • Apr. 16, 2026

Cyanide fishing has historically been used in parts of Southeast Asia to stun or kill fish, often for the live reef trade.

From BBC • Apr. 13, 2026

The tide was lower than expected, so the landing craft were hung up on a reef.

From The Wall Street Journal • Mar. 4, 2026

He said Fishguard residents had told him the ship could be left for scrap, while others believe it might become a reef.

From BBC • Feb. 17, 2026

Otters dove down and tore clams from the reef.

From "The Wild Robot Protects" by Peter Brown

Related Words

• atoll
• beach
• coral reef
• shoal