A Doriathrin word for “Elf” (Ety/ELED), also attested in its class plural form Eglath which was marked as both Doriathrin (Ety/ELED) and Ilkorin (Ety/GAT(H), LED). This word developed from the inverted primitive form ᴹ✶edel[a] of the root ᴹ√ELED (Ety/ELED). First the middle [e] was lost because of the Ilkorin syncope, after which the resulting [[ilk|[dl] became [gl]]].
This word was a frequent element in Ilkorin names. As noted by Helge Fauskanger (AL-Doriathrin/Eglador), ordinarily the [[ilk|primitive final [a] would be lost]] in Ilkorin. Perhaps it was preserved in Ilk. Egla by analogy with the various names where it appeared, or perhaps Egla was actually the genitival form (of unattested ✱Egol as Ilk. legol) with the suffix -a(n).
Conceptual Development: In the Gnomish Lexicon from the 1910s, G. Egla was the Gnomish word for “Elf”. In The Etymologies from the 1930s, Tolkien first wrote Ilk. Eld for “Elf”, derived from the uninverted form of the root. This was rejected in favor of Ilk. Egla, perhaps an attempt to preserve the earlier Gnomish form.