Guys, I think I may have a proper definition for the name of Uinen. Here's the logic behind it: It must be made of two parts, the second of which is NEN:water. So the first element is probably UI. This occurs in Uilos, which means Ever-snow(or Ever-white). Besides that, there is also the Quenya form OIO, in Oiolossë, Oiomúrë, etc.
So combining the two elemnts will result in UI+NEN: Ever-water. What do you think? should we write this in the Etymology section?