Согласно Этимологиям (5 том, стр. 356): эдель произошло от эльда, элед с перестановкой согласных.
ELED- go, depart, leave. Q Elda ‘departed’ Elf; N eledh. Q lesta- to leave, pa.t. lende. [This original entry was replaced by the following, written as carefully and clearly as the first:] ÉLED- ‘Star-folk’, Elf. Q Elda (Eldamar or Elende — Elvenhome, Eldalie, Eldarin); N Eledh, pl. Elidh, cf. Eledhrim, Eledhwen [Elf-fair >] Elf-maid, Elennor (Eledandore > Eleðndor). Dor. Eld, pl. Eldin. Dan. Elda. [The Dor. and Dan. forms were subsequently struck through and the following added:] In Dor. and Dan. transposed > edel- whence Dor. Egla, Eglath (cf. Eglamar, Eglorest); Dan. Edel. Eglador — Doriath in Doriathrin; Ariador = lands outside of Eglador. Cf. Eglor (Elf-river), Ilkorin name of a river in W. Beleriand. [On the earlier and later entries ELED see p. 344. Further faint pencillings show my father doubtful of the derivation of Eldar from a base meaning ‘star’, and suggesting that, although the name was so interpreted, it was probably in fact altered from edela ‘eldest’ - eðel, eðil being found also in Noldorin. A base EDE-, EDEL- ‘precede, come forward’ is proposed, with derivative edela (= eleda) ‘firstborn’, but this is struck out.]
То же из Сильмариллиона (стр.449)
êl, elen ‘star’. According to Elvish legend, ele was a primitive exclamation ‘behold!’ made by the Elves when they first saw the stars. From this origin derived the ancient words êl and elen, meaning ‘star’, and the adjectives elda and elena, meaning ‘of the stars'. These elements appear in a great many names. For the later use of the name Eldar see the Index. The Sindarin equivalent of Elda was Edhel (plural Edhil), q.v.; but the strictly corresponding form was Eledh, which occurs in Eledh-wen.
Так что корень Эль туда уже не входит. Это новое слово.
