I asked a similar question. I got a couple of references that I don't think answer the question, and then the question was closed. I then tried to find answers on my own and finally concluded that the answer is:
There are several popular etymologies, but nobody knows for sure.
I tried to answer my own question, but it seems you can't do that if the question is closed. What else to do but ask a similar question and answer that question?
matsolof
2010-09-26 10:59:28