reef

a submerged ridge of rock or coral near the surface of the water

a rocky region in the southern Transvaal in northeastern South Africa; contains rich gold deposits and coal and manganese

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

lower and bring partially inboard

reef the sailboat's mast

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