Tolkien used this root and ones like it for sprouting things for much of his life. Its earliest appearance was unglossed ᴱ√TUẎU in the Qenya Lexicon of the 1910s, where the Ẏ probably represents an ancient palatal spirant [ʝ] or [ç], with derivatives like ᴱQ. tuile “spring, (lit.) a budding” and ᴱQ. tuita- “to bud, burst, burgeon, grow” (QL/96). It also had derivatives in the contemporaneous Gnomish Lexicon such as G. tuil “spring” and G. tuitha- “sprout, spring, gush” (GL/71). In The Etymologies of the 1930s Tolkien gave the root as ᴹ√TUY “sprout, spring” with derivatives like ᴹQ. tuia-/N. tuia- “sprout, spring” and ᴹQ. tuile “spring-time” (Ety/TUY). The root reappeared several times in Tolkien’s later writings with glosses like “sprout” (PE19/54) and “sprout, bud” (VT39/7).
Primitive elvish
tup
root. cover over, hide
tuy
root. sprout, bud
dom
root. dark, dark, [ᴹ√] faint, dim
This root was the basis for the main Elvish words for “dusk, night”, which was established as Q. lómë in Quenya for most of Tolkien’s life. The earliest form of this root was ᴱ√LOMO in the Qenya Lexicon of the 1910s, unglossed but with various derivatives having to do with “dusk” and “shadow” (QL/55). One notable derivative was ᴱQ. lóme “dusk, gloom, darkness”, which survived in Tolkien’s later writings as “night” and in the 1910s was the basis for ᴱQ. Hisilóme/G. Hithlum “Shadowy Twilights”. Another notable derivative was G. lómin “shady, shadowy, gloomy; gloom(iness)” (GL/45) used in the name G. Dor Lómin, which in the 1910s was translated as “Land of Shadow” (LT1/112).
The “shadow” meaning of this early root seems to have transferred to ᴹ√LUM from The Etymologies of the 1930s, which served as the new basis for N. Hithlum (Ety/LUM), as opposed contemporaneous N. Dor-lómen which was redefined as “Land of Echoes (< ᴹ√LAM via Ilkorin or in later writings, via North Sindarin). The “dusk” sense was transferred to a new root ᴹ√DOM “faint, dim”, which (along with ᴹ√DOƷ) was the basis for the pair words ᴹQ. lóme/N. dû “night” (Ety/DOMO).
These two words for “night” survived in Tolkien’s later writing in both Quenya and Sindarin (Let/308; SA/dú). In notes from the 1940s Tolkien clarified that it “has no evil connotations; it is a word of peace and beauty and has none of the associations of fear or groping that, say, ‘dark’ has for us” (SD/306). The Elves were quite comfortable being under the night sky, dating back to the time when the Elves lived under the stars before the rising of the Sun and the Moon. The root √DOM reappeared in etymologies for star-words from the late 1950s or early 1960s (PE17/152). It appeared again in some very late notes from 1969 where it was glossed “dark” and served as the basis for words meaning “blind” as well as “night”, though this paragraph was rejected (PE22/153, note #50).
mornā
adjective. dark
du Reconstructed
root. dark
This root had to do with covering things for much of Tolkien’s life. The first appearance of the root was unglossed ᴱ√TUPU in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. tumpo “shed, barn” and ᴱQ. tupu- “roof, put lid on, put hat on, cover” (QL/95). Tolkien said this root was “much as TELE”, which in this document was glossed “cover in” (QL/90). The root ᴱ√TUPU also had derivatives in the contemporaneous Gnomish Lexicon such as G. tub- “cover” and G. tump “a shed” (GL/71).
In The Etymologies of the 1930s the root ᴹ√TUP was given as a variant of ᴹ√TOP “cover, roof” with derivatives like ᴹQ. tupse/N. taus “thatch” (Ety/TUP; EtyAC/TOP). In Tolkien’s later writings its most notable derivative was Q. untup- “cover (over)” as in Q. ar hísië untúpa Calaciryo míri oialë “and mist covers the jewels of Calacirya forever” (PE17/73; LotR/377). The root √TUP “cover over” itself was mentioned a couple times in Tolkien’s later writings (PE17/73), though in one place of these places it was given as √TUI “cover over, hide”, but since in that note it was the basis for primitive ✶Utupnu, this √TUI is clearly a malformed ✱√TUP (MR/69).