Reef
late 16th century (earlier as riff ): from Middle Low German and Middle Dutch rif, ref, from Old Norse rif, literally ‘rib’, used in the same sense; compare with reef2.
wiktionary
From earlier riff, from Middle English rif, from Old Norse rif(“rib, reef”), from Proto-Germanic *ribją(“rib, reef”), from Proto-Indo-European *h₁rebʰ-(“arch, ceiling, cover”). Dutch rif(“reef”), Low German riff, reff(“reef”), German Riff(“reef, ledge”) are also borrowed from Old Norse. Doublet of rib.
From Middle English ref, hreof, from Old English hrēof(“rough, scabby, leprous", also "a leper”), from Proto-Germanic *hreubaz(“rough, scabby, scrubby”), from Proto-Indo-European *kreup-(“scab, crust”), related to Old English hrēofla(“leprosy, leper”). Cognate with Scots reif(“a skin disease leaving crusts on the skin, the scab”), Old High German riob(“leprous, scabby, mangy”), Icelandic hrjúfur(“scabby, rough”). Compare riffe, dandruff.
etymonline
reef (n.1)
"low, narrow rock ridge underwater," 1580s, riffe, probably via Dutch riffe, from a Scandinavian source such as Old Norse rif "ridge in the sea; reef in a sail," literally "rib" (see rib (n.)). Also extended to the low islands formed by coral debris or to any extensive elevation of the bottom of the sea.
reef (n.2)
"horizontal section of sail rolled or folded" to reduce the area exposed to the wind, late 14c., rif (mid-14c. in rif-rope "rope used in tying down a reef"), from a Scandinavian source such as Old Norse rif "reef of a sail," probably a transferred use of rif "ridge under the sea; rib" (see rib (n.) and compare reef (n.1)). German reff, Swedish ref, Norwegian riv, Danish reb likely all are from the Old Norse word.
reef (v.)
1660s, "take in, roll up" (a section of a ship's sail or something like it, t reduce the extent of it), from reef (n.2). Later also in a general sense of "gather up stuff" of any kind (1836), hence the criminal slang sense of "to pick" (a pocket). Related: Reefed; reefing.
