[tied] Re: Ther Beaver and Its Teeth (Origin?)

From a book I read as a teenager (George Borrow's "Wild
Wales") I learned the Welsh word for beaver was "afanc".
Borrow, besides being a very entertaining writer, was an
amateur linguist who would fit nicely with some of the wilder
contributors to Cybalist. Writing in the 1850s, when
palaeontology was an exciting new field, he thought the name
had been transferred from the extinct British crocodile to the (I
believe now also extinct) British beaver.
I just looked up "beaver" in an online Welsh dictionary, and ,
by God, there was "afanc".
Since I've remembered this useless bit of information for fifty
years, can anyone give me an etymology for "afanc"?
Dan Milton