Reef

n. ridge of coral or rock located near the surface of the sea; part of a sail that can be adjusted in order to control the sail area that is exposed to the wind

v. roll up part of a sail in order to expose less sail area to the wind (Nautical)

In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water yet shallow enough to be a hazard to ships. Many reefs result from abiotic processes—deposition of sand, wave erosion planning down rock outcrops, and other natural processes—but the best-known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and calcareous algae.
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Noun
1. a rocky region in the southern Transvaal in northeastern South Africa; contains rich gold deposits and coal and manganese
(synonym) Witwatersrand, Rand
(hypernym) region, part
(part-holonym) Transvaal

Noun
1. a submerged ridge of rock or coral near the surface of the water
(hypernym) ridge
(hyponym) coral reef
Verb
1. lower and bring partially inboard; "reef the sailboat's mast"
(hypernym) lower, take down, let down, get down, bring down
2. roll up (a portion of a sail) in order to reduce its area
(hypernym) roll up, furl
3. reduce (a sail) by taking in a reef
(hypernym) shrink, reduce

n. reef, part of a sail that can be adjusted in order to control the sail area that is exposed to the wind

v. reef, shorten sail

(v. t.)
To reduce the extent of (as a sail) by roiling or folding a certain portion of it and making it fast to the yard or spar.
  

(v. t.)
That part of a sail which is taken in or let out by means of the reef points, in order to adapt the size of the sail to the force of the wind.
  

(n.)
A large vein of auriferous quartz; -- so called in Australia. Hence, any body of rock yielding valuable ore.
  

(n.)
A chain or range of rocks lying at or near the surface of the water. See Coral reefs, under Coral.