a submerged ridge of rock or coral near the surface of the water
"The divers spotted a hidden reef just beneath the waves, where schools of fish darted around the ancient coral structures."
a rocky region in the southern Transvaal in northeastern South Africa; contains rich gold deposits and coal and manganese
"Historical maps show that ancient mining operations were once established along the reef, exploiting its abundant gold, 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
"The sailor adjusted the reef on the mainsail to reduce its surface area as the storm winds picked up."
A chain or range of rocks, sand, or coral lying at or near the surface of the water.
"After swimming in the warm water, he began to suffer from an intense case of itches that felt like a prickly rash across his back."
The itch; any eruptive skin disorder.
In plain English: A reef is an underwater ridge of rocks that sticks up from the ocean floor and often blocks boats from passing through.
"We saw many colorful fish swimming near the coral reef during our dive."
Usage: As a noun, "reef" refers primarily to submerged rock formations that break waves and protect coastlines from erosion. While sailors use it as a verb meaning to reduce sail area in strong winds, this note focuses on the common geographical definition of underwater barriers or coral structures near the surface.
roll up (a portion of a sail) in order to reduce its area
"The sailor reefed the mainsail as the wind began to blow too strongly."
reduce (a sail) by taking in a reef
"The experienced sailor decided to reef the mainsail as the wind began to pick up."
To take in part of a sail in order to adapt the size of the sail to the force of the wind.
"The sailor reefed the mainsail before rounding the corner as the gale intensified."
In plain English: To reef means to pull up and secure loose parts of a sail on a boat so it catches less wind.
"The angry crowd began to reef up against each other when the argument started."
Scabby; scurvy.
"The old sailor's face was as red and reefy as a sore throat from drinking salted water."
The word reef comes from the Old Norse term rif, which originally meant "rib." It entered English through Middle English and is related to Dutch and Low German words that share this same meaning.