elda 1. originally adj. "of the stars", but wholly replaced (WJ:362) by: 2. noun (Elda) = one of the people of the Stars, (high-)elf, an Elf (SA:êl, elen, Letters:281, ELED, ÉLED; notice that Tolkien abandoned a former etymology with "depart"), chiefly in the pl. Eldar (WJ:362, cf. GAT(H), TELES).The primitive form Tolkien variously cited as ¤eledā / elenā(Letters:281, PE17:152) and ¤eldā(WJ:360). Partitive pl. Eldali (VT49:8), gen. pl. Eldaron (WJ:368, PM:395, 402);dative pl.eldain "for elves", for Eldar (FS); possessive sg. Eldava "Elf's" (WJ:407); possessive pl. Eldaiva (WJ:368), Eldaivë governing a plural word (WJ:369). The word Eldar properly refers to the non-Avari Elves only, but since Eldar rarely had any contact with the Avari, it could be used for "elves" in general (in LT1:251, Elda is simply glossed "Elf"). See also Eldo. The plural form Eldar should not require any article when the reference is to the entire people; i Eldar refers to a limited group, "(all) the Elves previously named"; nevertheless, Tolkien in some sources does use the article even where the reference seems to be generic (i Eldar or i-Eldar, VT49:8).
Quenya
elda
noun. Elf, (lit.) one of the Star-folk
elda
of the stars
elda-lambë
proper name. Language of the Eldar
Elda-lambë
the language of the eldar
Elda-lambë noun "the language of the Eldar" (WJ:368)
elena
of the stars
elena adj. "of the stars" (SA:êl, elen); also elenya
The most common Quenya word for “Elf”. Its literal meaning is “one of the Star-folk” (WJ/374), a name given to them by Oromë (S/49) and derived from the same primitive root √EL as Q. elen “star”. Strictly speaking, this term excludes the Avari who chose not to journey to Valinor, so that the proper term for all of Elvenkind is Q. Quendë “one of the Elven race”. The Elves of the West rarely encountered the Avari, however, so that term Elda was ordinarily broad enough to describe all Elves.
Conceptual Development: This word dates back to the earliest stages of Tolkien’s languages. At its first appearance, ᴱQ. Elda was glossed “a beach-fay” (QL/35), but was soon extended to describe all Elves (LT1/113). In Tolkien’s earliest writings the word was not given a clear etymology. In the Lhammas “Account of Tongues” from the 1930s (LR/168-180), Tolkien gave ᴹQ. Elda the sense of “one who departed” (LR/169), as opposed to the ᴹQ. Lembi “Lingerers” who remained behind (precursors of the Avari). With this sense, Elda was derived from ᴹ√LED “go, fare, travel” (Ety/LED).
Tolkien soon revised the etymology of Elda so that it was derived instead from ᴹ√ELED “star-folk” (Ety/ELED). In some later writings, he considered both etymologies of this word to be valid, so that Elda was blending of both “star-folk” (from √EL) and Q. Eldo “marcher” (from √LED or √DEL), as discussed in the Quendi and Eldar essay from 1959-60 and elsewhere (WJ/362-3, PE17/139). However, the sense “star-folk” is probably better known.
In some notes from 1957, Tolkien considered deriving this word from a variant root √DEL “fair” so that its meaning would be “the fair” (PE17/151), but this seems to have been a transient idea.