There is no known explanation for why the plural of mun is muz instead of muzze.

To correct some of Loniizrath's speculation, jul is the word for "mankind," whereas muz would be used to refer to "many men" but not "all men" or "all mankind".

I think Mun refers more to Mankind, and Muz is the more direct man/men. The same way Dov means Dragonkind whereas Dovah is for one or multiple dragons.

I might be wrong though. That was mostly speculation.

loniizrath - actually Jul is used for all of mankind. Mun is a man, singular. A dude. Muz is many men, a group. if you want to refer to mankind as race you would say Jul