In alchemy, Archeus, or archaeus, is a term used generally to refer to the lowest and most dense aspect of the astral plane which presides over the growth and continuation of all living beings. I'm guessing that they just used a bit of Latin, changed it up, and tied it in a bit more. It's an etyomology SF, so there's no way to tell which one is absolutely right. Besides, it's just a game.