I have three leading theories, two are reaching...
- Thal-mor, mor=dark/evil, thal=purify
- Thal-mora, mora=woods, thal=protector
- Thal-maor, maor=sea, thal-protector
3. The formation of the Thalmor was not an altruistic gesture, however: the Altmer sought to control Valenwood because the region, along with southern Hammerfell, harbored many pirate groups which threatened the shore of the Summerset Isles.
(I kind of doubt "mor" could have come from "mer" unless it is a weird grammatical thing that changes vowels which I don't think Aldmeris has).
Another stretch: "bala" means "power", but I can't see any clear route how "bala" could become "thal". "Fal" means "snow", so "thal" could mean "pure like snow" (about as "out there" as one cold get as far as theorizing!).
Yet another: "latta" "light" could be twisted around to mean "pure/purity", and "tal" could become "thal".
Some Altmer names from UESP that include "mor":
- Moranarg
- Mororurg
- Morgina (probably just taken from Morgana, a common-ish modern name)
- Morlia, Morlina, Mormia, Morna
- Morsara, Morsha, Mortha
- Morsephona
- Caemor/in, Camoran
- Stormor/in
- Thromor/in
And "thal", "tha", "thro", "thor"/"thar", or "tal":
- Mithron
- Throm- (a common prefix)
- Orthorn
- Larethor/in
- -tha/r (a common suffix)
- Larethal (only "thal")
- Estalenya
- Siltalaure
(I'm starting to think -in is either a diminutive or superlative marker).
Since Larethal is the only thing I found with "thal" in it, I tried to see what "Lare" could mean. Closest I came was similar to "mallari" (gold), which could actually come from "mala-lari", "high-lari", perhaps "high-metal". Another stretch... If Larethal actually comes from La-rethal then I'm at a loss, because "la" means "time" and there is no guess as to what "rethal" could be.
I find it odd that in the Ayleid language there is no use of "TH" unless it's in the word "math" (home). We have basically no Aldmeri words, and none that we have use "TH".
I'm even going to go as far as to wonder if "thal" isn't a play on "alt", just a meaningless shifting of sounds, and "mor" is the same with "mer".
But I like "wood/sea protector" best in the end. But if "Thalmor" is indeed a compound word, it would read "mor of the thal", in which case "woods/sea of the protector" doesn't make sense. Well, not as MUCH sense. "Thal" could mean "ruler" or "chosen" or something that would say "that sea/forest belongs to us".
It would also make sense if "Thalmor" was just someone's name once upon a time, as both elements can be found in some manner in names used in the various games.
And one more thought, "almo" is a common Altmer name element.