A word by any other name ...

[Bêthberry]

Gandalf did use a white light to chase off the Nazzies once on the Pelennor Fields, and so we can assume that he had knowledge of optics.

So says alatar on the Denethor's Plunge thread in Movies. alatar's nickname for the baddies got me thinking a bit (just a bit, so my question might be one of those out, out brief light kind of thing ).

What is the source for Tolkien's word Nazgul? How did Tolkien derive it? Why would he have picked it? It's his created language after all. Surely he would have been aware of just how similar a word it is to the name of the dreaded enemy of WW II, Nazi.

In the Forward to LotR, Tolkien denies that his story is any kind of allegory of the Second World War. He provides a fitting argument which dismisses any easy kind of equivalence between the Free Peoples of Middle-earth and the Allies of the Western World. So, if he didn't want readers to make this kind of connection, why did he employ a word for his baddies which is so similar to the name of the Allies' enemies?

We are so used to taking Tolkien's side here and defending his argument that LotR has little to do with the wars of his world. But can we blame readers for thinking along those lines when he allows such verbal similarity? It is almost a superficial propaganda.

If Gandalf had knowledge of 'optics', so certainly did Tolkien. What's with his use of Nazgul?