(rēf) noun
1. A ridge of sand or rocks, or especially of coral, at or near the surface of the water.
2. A lode, vein, or ledge.
3. A shoal. [<ON rif rib, reef]
—reef′y adjective

(rēf) Naut. noun
1. The part of a sail that is folded and secured or untied and let out in regulating its size on the mast.
2. The tuck taken in a sail when reefed.
—v.t.
1. To reduce (a sail) by folding a part and tying it round, and usually fastening it to, a yard or boom.
2. To shorten or lower, as a topmast by taking part of it in. [ME riff, prob. <ON rif rib]