Thread: Elfhelm, Marshal of Rohan
The Elves, being Firstborn and all, probably did not have any similar practice of nicknaming other Elves after heirlooms of other races (imagine: hey, "Dwarfnecklace!")
Just a guess. The name occurs in Primary World sources, and Leonid L. Korablev's The True Elves of Europe suggests a meaning (not necessarily in a Tolkien context, although '(cf. Elfhelm of Rohan)' is also noted): 'protected by Elves? (helm-protection by Elves)'. The site also notes:
Searle's "Onomasticon" (mentioned by Arundell Lowdham, a character of JRRT's "Notion Club Papers") contains 35 different names of the form AElf + adjective (noun); it mentions 75 recorded bearers of the name AElfwine "Elf-friend".
Elfhelm fits in with Tolkien using Old English to represent 'some name' in the actual language of the Rohirrim (Elfhild, Elfwine, for examples).