Gwath=Shadow
Vagor=Blade
Gwath + Vagor = Gwathagor = Shadowblade
I left out the 'v' because it is unnatural following the 'th', and that is what happens in RL linguistic development. Hard-to-pronounce letters get dropped.
I created the idea of Gwathagor Shadowblade the Warrior-Elf, I think, about 6 years ago while working on an RPG that never got off the ground. Fortunately it wasn't a total waste of time, as I hung onto the notion of Gwathagor, using the name now and then as a joke. Eventually he developed into my alter-ego in Middle-earth and now he's rather a fact of life. We got along, though. We're awfully similar.
I use it as my screen-name just about wherever I go on the internet, because it's invented, and therefore always available.