I think the first names that come to mind for this faction are things like The Void or The Ethereal . But those seems to be in common use accross a lot of things. Something similiar but a bit different might be The Dearth or older variations on the spelling of the word like Derthe or Dierth. The word dearth has some heft, feels like it is an established word that has fallen out of use/has been forgotten about, and carries with it a feeling of something ancient. Especially considering the origin and variations of the word according to Merriam Webster. It's a bit fitting for a seemingly forgotten ancient race that is shrouded a bit in mystery. It might have been an earlier term that this faction provided to lesser factions to help them grapple with the concept of who they were.