Gems of Long Lake (new discoveries)

[Guinevere]

Thank you for this interesting detail! I, for one, didn't know the meaning of "Dernhelm", but I'm not at all surprised. There must be many more such words which I'm sure Squatter knows about.

Btw, I recently discovered that there existed an Anglo-Saxon name Ælfstan meaning "Elfstone" . So the Elvish "Elessar" wasn't just made up but had an existing Anglo-Saxon origin, just as "Elendil" is equivalent to "Ælfwine" = Elf-Friend.
Tolkien apparently loved to invent possible explanations for such names.

Tolkien himself gives some explanations like the one about the ethymology of Smaug, in a letter from 1938:

The dragon bears as name – a pseudonym – the past tense of the primitive Germanic verb Smugan, to squeeze through a hole: a low philological jest.