Allow me to offer some alternatives!
-Yawning Abyss
-Gaping Abyss
-Thirsting Abyss
-Hateful Chasm
The rest is up to you! Abyss is definitely a strong word and theme to go with though. As for fluff, it depends on whether you want to give them a theme strictly linked to their name or not. Off the top of my head they could be a kabal from the worst slums of Commorragh (the ones where all the mandrakes and other foul beings reside) that have somehow carved out a relatively stable (by Commorrite standards) headquarters and maintain it as such by tossing slaves into a pit of deepest blackness, a sort of pact that lets them pay rent for living in such a dodgy neighbourhood.
For added originality; they hate this situation and are trapped in it, but are safe from the prying eyes of even Vect himself, and so their archon is something of a self-proclaimed prodigy that leaves The Eternal City only to capture more slaves and prolong his undisputed rule over an admittedly small and miserable kingdom.
Hope that helps!