https://en.wikipedia.org/wiki/Sabium Apparently it was the name of a king. I think it's kind of cool. It looked like a plant genus or something when I first saw it.
(I don't know if there's actually the name Sebastian in the Neverending Story. The main character is Bastian which is probably short for Sebastian but I don't think the book ever clarifies.) I wonder if Sabium came from Xayide somehow?