Drem yol lok. I just discovered this site today and am quite pleased that there are so many dedicated to speaking in dragon. I myself was transcribing the language into a notebook for my own practice, from the Elder Scrolls wikia, and no sooner did I finish than I discovered this site with over 2,500 words?! It's a nightmare! But a welcome one. I was hoping to be able to learn the language off the computer but now that looks impossible. I very much like that such effort has been taken to complete the language (I was going to make up new words myself), as in its canon state it can't support the construction of new random sentences very well. I have personally come up with a number of personal discoveries about the language, some of which I'll share.

First off, the word thu'um itself. I hope most of you realize that Odahviing pronounced this word "thurum" in the game, as the apostraphy clearly represents the omission of the "r" in "ur" - which by the way, for being a dovahzul character, is very rarely used. I personally believe several original words containing or ending in "u" are actually missing the apostraphy which would indicate the use of "ur". Moving ahead... my belief is that the word thu'um translates to "divine breath". I believe "thur" - overlord - can also be translated as "divine" or "god", from how it is used. (Does anyone know what Alduin meant when he named himself "Alduin Thuriin"?) As for breath, I note that su translates as "air" and su'um as "breath". If we suppose that dragons would define regular breath as "air-breath" (being that they often also breathe fire), and perhaps also that "su" is really "sur", we get surum or su'um. So now you see, why I believe thu'um means "divine breath"; I saw that "um" is here non-canonically translated as "around" and would like to see that changed. :)

I have a hypothetical proposition of another kind as well. Does anyone here play Magic: The Gathering? There is a group of dragons known as the "Primeval Dragons" whose names are said to be in "Old Draconic", corresponding to the dragon life stages:

http://wiki.mtgsalvation.com/article/Primeval_Dragons#Primeval_Dragons

http://wiki.mtgsalvation.com/article/Rhammidarigaaz

http://wiki.mtgsalvation.com/article/Rith

http://wiki.mtgsalvation.com/article/Treva

http://wiki.mtgsalvation.com/article/Dromar

http://wiki.mtgsalvation.com/article/Crosis

Note first that these names sound rather like dovahzul, including the "aaz" ending. What first caught my eye, though, was Crosis, who represents death. In dovahzul, krosis means "sorrow". In MTG, his full name is "Crosis, the Purger", and sorrow is one of the primary forms of purging one's soul, not to mention the obvious connection with death. I believe it's no accident - and that the authors of the respective examples did not necessarily know about the coincidense. Suffice it to say, you need a bit of belief in otherworldly dimensions and real dragon spirits from them in order to believe any of this - don't suppose we have any pagans running around here. Anyway, take it for what it's worth; I believe there may be actual dragons or dragon-friends inspiring these languages, and that makes it all the more worthy for me.

Drem yol lok!

A couple of things; there is a lot of variation in the pronunciations found in the game.  It's likely that Bethesda didn't have time to fully instruct the voice actors in correct pronunciations.  The pronunciation of thu'um with an "r" is heared nowhere else, not from the Greybeards, Paarthurnax, or Alduin, and it's well established that u'u is usually pronounced like oo.  Implying that thu'um is related to thur or su is a really big stretch.  However, the word su'um, breath, does use su as its root.

For more, here's a read on how the apostrophe in Dovahzul doesn't actually exist at all.

On a side note, "Alduin Thurii" (without the n, which I'm guessing is a typo), means "Alduin, his/her/its overlord".

And thanks for sharing the MTG names!  That's a neat coincidence.  It probably stems from the fact that both names are inspired by Old Englih or related Germanic languages, usually used in fantasy to draw upon a sense of something feeling old or ancient.

:-/ Well I'm sorry we disagree on this. I'm still fully convinced that thu'um is short for thurum since it is said in the game. It's a simple matter of common omission as the apostraphy clearly indicates. I don't see how it could be interpretted another way except by intentionally igorning what's there. But, dreh ol hi drem.

Fildovah

I don't see how it could be interpretted another way except by intentionally igorning what's there.

Generalizing that thu'um definitively stands for thurum requires you to ignore every other instance where it's pronounced thoom, which is all other times it's pronounced except the one instance you've pointed out.  If it were true, then su'um would also be pronounced surum, or zu'u would be pronounced zuru, but they never are.

Here is Odahviing pronouncing it as thoom. 
Here is Paarthurnax pronouncing it as thoom. 
Here is Arngeir pronounced it as thoom.

The theory is fine, but there's very little evidence holding it up.  I wouldn't look too deeply into in-game pronunciations since they aren't always consistent.

Edit: A better theory might be to say that Odahviing speaks a particular dialect where u'u can be pronounced uru.  This would explain the one pronunciation, and at the same time wouldn't compromise the language as a whole.