On page 22 of Kurt Vonnegut's darkly whimsical novel Breakfast of Champions, he claims that the word beaver meaning "vagina" originated among news photographers, who used it as a code word to tell other men that you could see up a woman's skirt from that angle. I don't know where he got that from, but I can't find any sources on that. The euphemism seems to trace back to 1910s British slang, when it referred to a man's beard. By 1927, due to the visual similarity, the definition got extended to female genitalia. The "beard" meaning emerged because of a resemblance to beaver pelts, and that word goes back to Old English beofor. Even earlier, beofor is from (through Proto-Germanic) the Proto-Indo-European root bher, meaning "bright" or "brown". Usage of beaver in language over time peaked in the 1850s, and the Vonnegutian definition is, in conclusion, erroneous.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.