I wonder if the Tolkien version has taken over , at least with "elves" because I hear and read a lot more about Santa's elves than I do Santa's elfs.
Also, the adjectival form of elf is elfin, not elven (just looked it up a few days ago).
As for "dwarf": when I first read FOTR Gandlaf refers to Khazad-dum as "Dwarrowdelf ".
I knew "delf" was the OE word for delve, but I was curious about "dwarrow".
It's the plural of dwarf.
I've attached the Wikipedia section about it.
The entire entry is here:
http://en.wikipedia.org/wiki/Dwarf_%28Middle-earth%29
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Spelling "Dwarves"
The original editor of The Hobbit "corrected" Tolkien's plural dwarves to dwarfs, as did the editor of the Puffin paperback edition of The Hobbit.[14] According to Tolkien, the "real 'historical'" plural of dwarf is dwarrows or dwerrows.[15] He referred to dwarves as "a piece of private bad grammar".[16] In Appendix F of The Lord of the Rings it is e xp lained that if we still spoke of dwarves regularly, English might have retained a special plural for the word dwarf as with goose—geese. Despite Tolkien's fondness for it, the form dwarrow only appears in his writing as Dwarrowdelf, a name for Moria.
Tolkien used Dwarves, instead, which corresponds with Elf and Elves. In this matter, one has to consider the fact that the etymological development of the term dwarf differs from the similar-sounding word scarf (plural scarves). The English word is related to old Norse dvergr, which, in the other case, would have had the form dvorgr. But this word was never recorded, and the f/g-emendation (English/Norse) dates further back in language history.
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I prefer Tolkien's versions.