reef

(noun) a submerged ridge of rock or coral near the surface of the water.

(noun) a rocky region in the southern Transvaal in northeastern South Africa; contains rich gold deposits and coal and manganese. Synonyms: Witwatersrand, Rand, Reef.

(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.

(verb) lower and bring partially inboard. Example: "Reef the sailboat's mast."

(verb) roll up (a portion of a sail) in order to reduce its area.

(verb) reduce (a sail) by taking in a reef.