Interesting! I wrote an answer here.
I guess I'll leave my response here. In general, I am very interested in getting to the actual answer. But it seems to me that none of the guesses are getting close to anything like proof, i.e. citations from early Yiddish source, etc.
In the end, many intelligent people made a lot of educated guesses. Which is fine, and I appreciate that because it shows a "folk" love of etymology.
Commenting by HaloScan
