Reef is defined as a ridge of coral, alga, sand or rock close to the surface of the water in the ocean.(noun)
An example of a reef is the Great Barrier Reef which was formed when the sea levels rose, flooding the continental shelf of Australia, allowing the coral that were growing on the edges of the shelf to grow and begin form the reef.
The definition of a reef is part of a boat's sail that can be rolled and tied to cut down on wind resistance.(noun)
An example of a reef is the rolled up part of a sail during a storm at sea.
See reef in Webster's New World College Dictionary
Origin: prob. via Du or MLowG rif < ON, lit., rib
Origin: ME riff < or akin to ON rif (< IE *reip-, a strip < base *rei-, to tear, cut > rive): orig. used of cords for reefing
See reef in American Heritage Dictionary 4
Origin: Obsolete Dutch rif
Origin: , possibly from Old Norse, ridge.
Origin: Middle English riff
Origin: , from Old Norse rif, ridge, reef.
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