Yours, Etc.: Origins and Uses of 8 Sign-Offs
Old English byht "bend, angle, corner" (related to bow), from Proto-Germanic *buhtiz (cf. Middle Low German bucht, German Bucht, Dutch bocht, Danish bught "bight, bay"), from PIE root *bheug- (3) "to bend," with derivatives referring to bent, pliable, or curved objects (cf. Old English beag, Old High German boug "ring;" see bow (v.)). Sense of "indentation on a coastline" is from late 15c.