The root ᴱ√Ū⁽¹⁾ “under” appeared in the Qenya Lexicon of the 1910s as a reduced form of {ᴱ√UGU >>} ᴱ√UƷU, with derivatives like ᴱQ. ū “beneath” and ᴱQ. umbe “dale, dell” (QL/96-97). It also had derivatives in the contemporaneous Gnomish Lexicon such as G. um⁽⁾ “lowlying” and G. umbel “a dell” (GL/74). Tolkien noted that ᴱ√Ū also meant “not”, and contrasted ᴱ√Ū¹ “under” with ᴱ√NŪ (ᴱ√NUHU) of similar meaning (QL/68, 96). Indeed, in Tolkien’s later writings, √NŪ/UNU was the usual basis for “under” words, and ᴱ√Ū¹ “under” seems to have been abandoned.
Early Primitive Elvish
nō
root. become, be born
yo(no) Reconstructed
root. YO(NO)
ū
root. not
vo(no) Reconstructed
root. son
maþa
root. dusk
ū
root. under
kulu
root. gold
kulū
noun. gold
ī
root. be
This root was given as ᴱ√MASA¹ “dusk” in its main entry in the Qenya Lexicon of the 1910s, but its Gnomish form math- indicates the true root was ᴱ√MAÞA (QL/59). This was clarified in a list of roots at the end of the M-section in the Qenya Lexicon (QL/63) and its representation as maþ- in the contemporaneous Gnomish Lexicon (GL/59). Its most notable use in the legendarium was in the name G. Umboth-muilin “Pools (muil-plural) of Twilight (umboth)”, where G. umboth or umbath “nightfall” was derived from a strengthened form of the root, ᴱ√mbaþ- (GL/75). However, in later writings this name was reconceived as Ilk. Umboth Muilin “Veiled (muilin) Pool (umboth)”, with the first element umboth meaning “large pool” (Ety/MBOTH, MUY). The name was ultimately replaced with S. Aelin-uial (S/114), by which point the early root ᴱ√MAÞA was long abandoned.