Oswin means “God’s Friend” which I find very sweet. Originally Oswine, it’s the name of a King in Deira. He ruled peacefully for seven years but then Oswiu, the king to the North declared war on him. Oswine refused to engage, but was ultimately betrayed by his friend and put to death.
This is pretty much all I can find on Oswin, sadly. So I’ll just add that Winnie, O and my favorite, Ozzy are all wonderful nicknames!