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 reef is home to a small Philippine military outpost aboard the BRP Sierra Madre, a rusting World War Two-era ship deliberately grounded there in 1999 to assert Manila's claim to the territory.

From BBC • Apr. 13, 2026

Martindale and her research team, including Stéphane Bodin of Aarhus University, were exploring the rugged valley to study the ecology of ancient reef systems that once existed there when the area lay beneath the ocean.

From Science Daily • Mar. 8, 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

I did it three more times and became exactly like a dolphin, grazing the sharp reef of pool steps.

From "Everything Sad Is Untrue" by Daniel Nayeri

Related Words

• atoll
• beach
• coral reef
• shoal