A Sindarin noun for a source of water (RC/772). It appeared as an element in several names, such as Mitheithel, the Sindarin name for the river Hoarwell (LotR/200). From its glosses, it seems it could apply to a variety of water sources, including springs, wells and fountains (RC/772, SA/eithel, LR/301). It was derived from the primitive form ✶et-kelē, literally “out-flow”, but in ancient times the [tk] was transposed to [kt] giving ektelē* (SA/kel, Ety/KEL). In Sindarin, this pair of voiceless stops became spirants [xθ], and then the [[s|[x] vocalized to [i]]] to form the diphthong [ei].
Conceptual Development: In the Gnomish Lexicon from the 1910s, there were two distinct precursors to this word, G. aithl “spring” and G. ecthel(uin) “fountain, fount” (GL/18, 25, 31). In Early Noldorin wordlist from the 1920s, there was an additional form ᴱN. eithlos with several variants (PE13/142, 158). In The Etymologies from the 1930s, these seem to have been combined into N. eithel (Ety/KEL), and this is the source of derivation given above. All of the earlier forms seem to broadly have the same etymology, and so the changes represent the evolving phonetic development of the languages.