I’m afraid you’re looking for know one.
Point is, Eldian as defined in Fantastic Four 126 (1965): a person born in the country of Eldia, an almost utopian society (now gone) on which the Earth’s sun never shines. Hence it was always dusk there—hence its name (etymology unknown). From nova to new dark “don’t make me call your mom.”
Regardless of what and where they are now, it sounds like they should be proud of their past. They were day-less nigh-tarians. Dayless nightarians? Okay my editor just made that up but I’m not changing it though because he gets mad when I change his words!