luff (n.) Look up luff at
also loof, in sailing, c. 1200, "contrivance for altering a ship's course," also "part of a ship's bow where the sides begin to curve," from Old French lof "spar," or some other nautical device, "point of sail," also "windward side," of uncertain origin and sense development, probably ultimately from Germanic (compare Middle Dutch lof "windward side of a ship" (Dutch loef), which might also be the direct source of the English word).

This is from Proto-Germanic *lofo (source also of Old Norse lofi, Gothic lofa "palm of the hand," Danish lab, Swedish labb "paw"), from PIE *lep- (2) "to be flat" (see glove (n.)). As a verb, "bring the head of a sailing-ship nearer the wind," from late 14c., from the noun.