beaver - O.E. beofor (earlier bebr), from P.Gmc. *bebruz (cf. Low Ger. bever, O.H.G. bibar), from PIE *bhebhrus, reduplication of base *bhru- "brown" (cf. Lith. bebrus, Czech bobr, Welsh befer, see bear (n.) for 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.
from Online Etymology Dictionary