1911 Encyclopædia Britannica/Reef

REEF (1) (Du. rif, cf. Ger. Riff, Swed. ref, &c., all from O. Nor. rif, rib), in physical geography, a narrow ridge of rock, shingle or sand culminating at or near the surface of the sea. In a transformed sense the word is used in mining of a vein or lode of gold-bearing quartz; (2) (Du. reef, rif, cf. Ger. Reff, Swed. raf, O. Nor. rif, possibly a transferred sense of rif, rib), a part of a sail which can be rolled or folded up, thus diminishing the amount of canvas spread to the wind. In square sails, “reefs” are taken from the top, in fore-and-aft sails from the foot.