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."

Definitions of reef
  1. noun
    a submerged ridge of rock or coral near the surface of the water
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    an atoll in the Marshall Islands; formerly used by the United States as a site for testing nuclear weapons
    an atoll in the Marshall Islands; site of an amphibious assault in World War II; later used temporarily by the United States to test atomic bombs
    an atoll in the western Marshall Islands that was used as a Japanese air and naval base during World War II
    Midway Islands
    an atoll in the Hawaiian Islands some 1300 miles to the northwest of Honolulu; site of an important United States naval base
    Great Barrier Reef
    the largest coral reef in the world; in the Coral Sea off the northeastern coast of Australia
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    coral reef
    a reef consisting of coral consolidated into limestone
    an island consisting of a circular coral reef surrounding a lagoon
    barrier reef
    a long coral reef near and parallel to the shore
    Florida key, cay, key
    a coral reef off the southern coast of Florida
    type of:
    a long narrow natural elevation or striation
  2. noun
    one of several strips across a sail that can be taken in or rolled up to lessen the area of the sail that is exposed to the wind
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    type of:
    slip, strip
    artifact consisting of a narrow flat piece of material
  3. verb
    roll up (a portion of a sail) in order to reduce its area
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    type of:
    furl, roll up
    form into a cylinder by rolling
  4. verb
    reduce (a sail) by taking in a reef
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    type of:
    reduce, shrink
    reduce in size; reduce physically
  5. verb
    lower and bring partially inboard
    reef the sailboat's mast”
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    type of:
    bring down, get down, let down, lower, take down
    move something or somebody to a lower position
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