In at least one Planescape book (In the Hellbound boxed set, I believe - maybe "The dark of the war", unless it was "Faces of evil"), the Tanar'ri are referred to as "the brood of Tanar". Which makes me wonder: who or what is Tanar?
- An ancient proto-demon who spawned the rest of the race? If so, does he/she/it still exist?
- Another name for the Abyss, which the race of Tanar'ri take their name from, the same way Baatezu are named after Baator? (In other words, maybe "Tanar" is simply the Abyssal word for
"Abyss"?)
- Something else entirely?
That's from a 3rd party source, the Slayer's Guide to Demons. I don't remember any Planescape book that uses the term. I like it, tough it's a bit monolithic for a plane of chaos.