I've seen the claim that those terms are Ayleid a couple of times, but the only book to mention them says no such thing. Source?
http://www.uesp.net/wiki/Lore:Ayleid_Language Fell for the [censored] trap.
Looking at it myself, it seems to be a inference on their part that its Ayleid, drawing on Ayleid ruin names. Looks like they got "math" as "home" from Mathmeldi, translated in Ayleid Inscriptions and their Translations, and then connected the word to the Ayleid dungeon Morimath, and then applied in The Wild Elves' translation of "Moriche" as "dark". And then got "dark home" as the translation of Morimath.
Honestly, though, it looks like they were just pre-Redguard fancy-lore-names for the Elves before they were retconned (as Morrowind's On Wild Elves shows) into the modern Dunmer, Altmer, Bosmer.