tumba noun "deep valley" (Letters:308; SA:tum and TUB gives tumbo "valley, deep valley"); apparently an extended form *tumbalë in tumbalemorna "deepvalleyblack" or (according to SA:tum) "black deep valley", also tumbaletaurëa "deepvalleyforested"; see Taurelilómëa-tumbalemorna...
Quenya
tumbalë
noun. depth, deep valley
tumba
adjective. deep valley, [ᴹQ.] deep, lowlying; [Q.] deep valley
tumba
deep valley
tumbalemorna
proper name. deepvalleyblack
A descriptive name of Fangorn appearing in the even longer Entish description of that land: Taurelilómëa-tumbalemorna Tumbaletaurëa Lómëanor (LotR/467). The name is a combination of tumbalë “deep valley, depth” and morna “black” (LotR/1131, PE17/81).
tumbaletaurëa
proper name. Deepvalleyforested
A descriptive name of Fangorn appearing in the even longer Entish description of that land: Taurelilómëa-tumbalemorna Tumbaletaurëa Lómëanor (LotR/467). The name is a combination of tumbalë “deep valley, depth” and taurëa “forested” (LotR/1131, PE17/80).
taurëa
adjective. forested
A word for “forested” appearing in the Entish phrase Tumbaletaurëa “Deepvalleyforested” (LotR/1131), it is simply the adjective form of taurë “forest”.
morna
dark, black
morna adj. "dark, black" (Letters:282, LT1:261; also used of black hair, PE17:154), or "gloomy, sombre" (MOR). Used as noun in the phrase mi…morna of someone clad "in…black" (PE17:71). In tumbalemorna (Letters:282), q.v. Pl. mornë in Markirya**(the first version of this poem had "green rocks", MC:215, changed to ondolisse mornë** "upon dark rocks" in the final version; see MC:220, note 8).
taurëa
forested
#taurëa adj. "forested" in Tumbaletaurëa, see Taurelilómëa-tumbalemorna...
hróva
dark, dark brown
hróva adj. "dark, dark brown", used to refer to hair (PE17:154)
lóna
dark
?lóna (4) adj. "dark" (DO3/DŌ). If this is to be the cognate of "Noldorin"/Sindarin dûr, as the context seems to indicate, lóna is likely a misreading for *lóra in Tolkien's manuscript.
lúna
dark
lúna adj. *"dark" in Lúnaturco and Taras Lúna, Quenya names of Barad-dûr (Dark Tower). (PE17:22). In the Etymologies, lúnë "blue" was changed by Tolkien from lúna (VT45:29).
lúrëa
dark, overcast
lúrëa adj. "dark, overcast" (LT1:259)
mori-
dark, black
mori- "dark, black" in a number of compounds (independent form morë, q.v.):Morimando "Dark Mando" = Mandos (MBAD, VT45:33), morimaitë "black-handed" (LotR3:VI ch. 6, VT49:42). Moriquendi "Dark Elves" (SA:mor, WJ:361, 373), Moringotto "Black Foe", Sindarin Morgoth, later name of Melkor. The oldest form is said to have been Moriñgotho (MR:194). In late material, Tolkien is seen to consider both Moringotto and Moricotto _("k") _as the Quenya form of the name Morgoth (VT49:24-25; Moricotto also appears in the ablative, Moricottollo). Morion "the dark one", a title of Morgoth (FS). Morifinwë "dark Finwë", masc. name; he was called Caranthir in Sindarin (short Quenya name Moryo). (PM:353) In the name Morinehtar, translated "Darkness-slayer", the initial element is defined would thus seem to signify "darkness" rather than "dark" as an adjective (see mórë). (PM:384, 385)
morĭ
adjective. dark
PQ. dark
móri
dark
móri adj. "dark" (MC:221; this is "Qenya"; in Tolkien's later Quenya mórë, morë)
nulla
dark, dusky, obscure
nulla adj. "dark, dusky, obscure" (NDUL), "secret" (DUL). See also VT45:11.
núla
dark, occult, mysterious
núla ("ñ")adj. "dark, occult, mysterious" (PE17:125)
ulca
adjective. dark
dark, gloomy, sinister
The adjective ᴹQ. tumba “deep, lowlying” appeared in rough (and ultimately rejected) notes on irregular verbs from the Quenya Verbal System of the late 1940s as a derivative of ᴹ√TUB “fall low, go down” (PE22/127). In a 1961 letter to Rhona Beare tumba was glossed “deep valley” as an element in the Entish phrase Q. Taurelilómëa-tumbalemorna Tumbaletaurëa Lómëanor “Forestmanyshadowed-deepvalleyblack Deepvalleyforested Gloomyland” (Let/308; LotR/467), but I think this is only an approximate translation, and the word is better understood as adjectival in sense: “✱like a deep valley”. As further evidence of this, in notes from the late 1960s the form tumba was changed to a more typical noun form Q. tumbo in the name Q. i Tumbo Tarmacorto “the Vale of the High Mountain Circle” (NM/351).
Neo-Quenya: For purposes of Neo-Quenya, I’d treat this word as an adjective only, and use Q. tumbo for the noun.