Nahfahlaar's name is one a few that has no known translation.

There are a couple ways the name could be broken up: Nah + Fah + Laar, Nah + Fahl + Aar, or even something like Nah + Fahlaar. Nah + Fahl + Aar does make a lot of sense given Nahfahlaar/Nafaalilargus's history.

Unfortunately fahl has no known translation. There is a possessive suffix -l/-iil (ziil 'your spirit'), but this really can't apply to a preposition like fah 'for'. Structurally similar word are nahl 'living' and wahl 'to build/raise/create'.

Here's an old thread discussing the name, though my old musings are really a stretch.

thanks for clearing that up for me

I was so happy to find this/Paarthie's old (locked) post about this topic. (And yes I am absolutely "necroing" this topic, so there.)

This is frustrating, just like the Dov Ah Kiin / Dovah Kiin mindboggle. Honestly, both are probably correct. And why not, as the Dragonborn is at once both and neither mortal and dragon. 

So maybe in this case, both possibilities are correct.

Either way you have a mercenary dragon who is called "Fury for/on behalf of ____" or "Fury ___ servant". Both work. But the former has a stronger connotation as the dragon was essentially hired. Or was he? Maybe the lore says he was hired but in reality he was enslaved or for whatever reason made himself a servant. Nahfahlaar did "escape" though according to the Atlas of Dragons, leaning toward the servant angle.

I too tried to think of what Laar might mean for all three, what Um might mean for the lake twins. I thought then maybe that was too easy, and likely none of those terms means anything to do with a lake or their literal position. 

We know dragons can share name elements. Nahfahlaar and Nahagliiv (Nah). Paarthurnax and Vulthuryol (Thur). Nahfahlaar and Sahrotaar (Aar). 

We should also keep in mind other translated dragon names. Do other dragons have prepositions in their names? (as in Fah). No. All known dragon name translations have strong speech elements (noun/adj/verb). 

So if Nah Fah Laar is grammatically improbable for a dragon name, then it has to be Nah Fahl Aar. 

That just leaves the translation, which honestly could be anything.

I forgot to mention in the previous post that Aar is in another dragon name, Sahrotaar.

Yoooo.....

So, about Fahl.

In line with Wahl-Wahlaan (to build-built) and Nahl-Nahlaas (living-alive), what about Fahl-Fahluaan?

If Fahluaan is "one who gardens" (or cultivates, which does not only correspond to crops) - as in the given example, the Gardener of Men is Hermaeus Mora who collects souls...

would, could not Fahl mean "garden" (n/v) or "grown/cultivated" (part.)? Or, loosely, "collect/ed" or even "care/d (for)"?

Nah Fahl Aar as Fury Garden Servent follows known dragon name grammar (as a noun/adj/verb). It doesn't make much sense, sure, but nor does Odahviing have anything to do with "snow" for what we know.