[Arvegil145]

Alliteration is a factor in the choosing of the names of course, but it's rare for Tolkien to use broken references that are TRULY broken. I mean, whenever he mentions certain characters, items, events, etc. fleetingly without any other mention of them inside a text, there is almost always something written about them outside of the text in which they are mentioned, or at least he has an idea inside his head to what those names should refer to.

For example, when Elrond mentions Hador, Túrin and Beren in The Lord of the Rings the reader doesn't know (at least those readers before The Silmarillion was published back in 1977) anything about who these characters were, yet since the name of Beren, for example, hales all the way back to The Book of Lost Tales, written many decades before The Lord of the Rings was published, the character of Beren is very much present, and fleshed out in Tolkien's mind.

The names I mentioned in the original post are, as far as I can remember, the only such cases in his writings. Naturally, considering their only appearance is in the form of a name invoked in a spell, nothing for certain can be told about who and what they might be, but speculate we can.

You brought an interesting point about the etymology, too. As languages are not my forte, I cannot say much in that respect.

All replies are more than welcome!