In addition, i'm curious about the Barsaebic Ayleids and the Cantemiric Velothi. Mostly because i'm unsure what "Barsaebic" or "Cantemiric" means, but also there's the fact that the C. Velothi are referred to as Velothi, instead of Chimer or Dunmer. The usage of "Velothi" confuses me a little, since if i'm not mistaken, the Ashlanders attach a slightly different meaning to the word. It's been ages since i've played Morrowind, so i'm not totally sure, but what were these Cantemiric Velothi, exactly? Altmer, Chimer or Dunmer (some kind of Ashlander, maybe)?
"Barsaebic" and "Cantemiric" are probably nothing more than geographically/culturally influenced names, given to them so they'll be more easilt separated from their namesakes when talking about them. Though, as I think of it, "Cantemiric" sounds a lot like "Cantemer-ic".
As for the Velothi.. The short story is this: "Chimer" was originally the name of the Aldmer who listened and followed Veloths teachings and philosophies. "Velothi" is the name given to the Chimer who followed Veloth when on his journey towards Morrowind. Not all Chimer did, and as a concequence, there are still Chimer living in Summerset to this day.
From http://www.imperial-library.info/obscure_text/nu-hatta_nu-mantia.shtml#8:
Just like the earliest Chimer who orphaned themselves from the Velothi Exodites, but remain Chimer today
The "Cantemiric" Velothi probably separated themselves from the major group of Velothi, and perhaps they differed in their opinion on Veloth's teachings, on their way towards Morrowind. Instead, they travelled south, into the Black Marsh. Perhaps, and the following completely lacks any evidence or grounding, their leader was called Cante (Cante-meri Velothi, get it? :frog: )
Though I'm just letting my thoughts stray. "Cante" sounds awful as a name for an elf, especially an Altmer, and I still favour the geography stuff.
Finally, my Ta'agra is a little rusty, but I find the Lilmothiit very, very interesting. The "-iit" suffix implies that they're related to Khajiit (the Pocket Guide suggests a relation too), yet they're supposedly fox-like. Are they another breed of Khajiit, born under a certain phase of the moons, or are they separate to the Khajiit of Elsweyr, with their own variety of forms? (Or do they even have other forms at all?)
Lilmothiit does sound very Khajiit-ish. It is possible that they shared the same culture, or at least were very close to each other, but I do not think the fox people are another breed of Khajiit.
There are a few, and quite unreliable, hints that there were once a lot more beastfolk in Tamriell. Except for the Akaviri beast peoples, we have the birdmen and "early orcs" from the http://www.imperial-library.info/obbooks/father_niben.shtml. Father of the Niben has several factual errors, though, and can't be trusted, but I like the thought of Birdfolk ruling Cyrodiil. Especially when you take the Ayelidi obsession with birds into account.
Then there's the fact that "Lilmoth" doesn't sound particularly Ta'agra-ish at all. There's a town called Lilmoth in Black Marsh that I presume they're responsible for building, just like Blackrose.
Since "-iit" means something along the lines of a job or a home (according to an interview with Jobasha), and "Khaj" is "desert", I'm guessing "Lilmothiit" means "one from Lilmoth" (the most likely translation) or "one who Lilmoths", but i'm confused as to what exactly "Lilmoth" means.
It certainly doesn't even sound very Argonian in origin (same goes for Blackrose)!
The part about "Lilmoth" could just come down to that "Lilmothiit" were another race, maybe with a slightly distinguished culture, but still related. You're most likely right that "Lilmothiit" means "one from Lilmoth", and if I were to guess, I'd say "Lilmoth" translates into something like "swamp", "djungle", or something else Black Marsh-related.
As for Blackrose, and the other places like it, I'd say it's just an Imperial translation of the original name. Or perhaps more likely a renaming.