Does anybody know why it's with a sin?


It's simply an outcome of the accent which many had (especially in Lithuanian and Belarussian neighborhoods) in pronouncing the shin altogether. Many couldn't pronounce it fully so it either came out like a sin or something in the middle (which kind of sounds as if the shin and sin collide as the letter in being said). Just don't ask why the first shin of this word wasn't confused the same way...lol, I don't even think those from their own region could explain the phenomenon of this outcome! ;-)