A word for “drear” or perhaps “*dreariness” (see below), attested only as an element in S. Emyn Muil “Drear Hills”.

Conceptual Development: The earliest iteration of this word was G. muil “tarn” [mountain lake] in the Gnomish Lexicon of the 1910s (GL/58), an element in the name G. Umboth-muilin where the first element was “twilight” and the second “pools” (LT2/225). In The Etymologies of the 1930s, Tolkien gave the Doriathrin/Ilkorin word muil “twilight, shadow, vagueness” from the root ᴹ√MUY (Ety/MUL), still an element in Umboth Muilin “Twilight Meres”, but now with the meaning of the elements reversed. In later writings, Tolkien changed this name to Aelin-uial, but muil in Emyn Muil might be a remnant of the Ilkorin word.

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”.

A Doriathrin noun meaning “twilight, shadow, vagueness” derived from root ᴹ√MUY (Ety/MUY). Its Quenya cognate ᴹQ. muile suggests a primitive form of *✶muı̯lē [mujlē].

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”.

A word appearing in the Gnomish Lexicon glossed “tarn” (GL/58). Its etymology is unclear. In later writings, muil had a number of different meanings.