S. muil n. and adj. “drear[iness]”
In later writings, this word is attested only as an element in S. Emyn Muil “Drear Hills”.
Conceptual Development: @@@
Possible Etymology: From our only late example, the word muil seems to be a (plural) adjective meaning “drear”. However, an adjective in this position beginning with m- would ordinarily undergo lenition to *vuil. If it is an adjective, its primitive form must have begun with mb-, which would have produced m- after mutation. If so, its unmutated singular form would have been either *bûl or *buil.
It seems likelier to me that muil is a noun, a remnant of earlier Ilk. muil “twilight, shadow, vagueness”, derived from the same root ᴹ√MUY. If so, the literal meaning of S. Emyn Muil would be “*Hills of Twilight” or perhaps “*Hills of Dreariness”.
Reference ✧ RC/334 ✧ Muil “drear”
Ilk. muil n. “twilight, shadow, vagueness”
Conceptual Development: Tolkien seems to have coined this word to explain Umboth Muilin “Twilight Meres”, a remnant of earlier G. Umboth-muilin “Pools of Twilight”. The meaning of the Ilkorin elements is reversed from the earlier name: in the Gnomish name muilin “pools” was the plural form of the word G. muil, glossed “tarn” in the Gnomish Lexicon (GL/58) which is an older English word for “(mountain) lake”. In later writings, Tolkien replaced this name with S. Aelin-uial “Meres of Twilight”.
Reference ✧ Ety/MUY ✧ Dor. muil “twilight, shadow, vagueness”
|ᴹ√MUY > muil||[mujlē] > [muilē] > [muile] > [muil]||✧ Ety/MUY|