Yours, Etc.: Origins and Uses of 8 Sign-Offs
Old English beofor, befer (earlier bebr), from Proto-Germanic *bebruz (cf. Old Saxon bibar, Old Norse bjorr, Middle Dutch and Dutch bever, Low German bever, Old High German bibar, German Biber), from PIE *bhebhrus, reduplication of root *bher- (3) "brown, bright" (cf. Lithuanian bebrus, Czech bobr, Welsh befer; see bear (n.) for the likely reason for this). Gynecological sense ("female genitals, especially with a display of pubic hair") is 1927 British slang, transferred from earlier meaning "a bearded man" (1910), from the appearance of split beaver pelts.