√RUK “terrible shapes and the fear they inspire, [ᴹ√] demon”; ᴹ√OROK “*goblin”
The root ᴹ√RUK “demon” appeared in The Etymologies of the 1930s with derivatives ᴹQ. rauko and N. rhaug of the same meaning, serving as the basis for N. Balrog (Ety/RUK). In the Qenya Lexicon of the 1910s, similar “demon” words were derived from primitive ᴱ✶ʒǝroukē instead (QL/32). As for √RUK, in the Quendi and Eldar essay of 1959-60 it was glossed “terrible shapes and the fear they inspire”, serving as the basis for both Q. rauko/S. raug “demon” and S. orch “Orc” < *urkō or *urkā (WJ/389-90, 415); the latter was instead derived from unglossed ᴹ√OROK in The Etymologies of the 1930s along with various other words for “goblin” in multiple Elvish languages (Ety/ÓROK). Primitive (o)rok reappeared in notes probably from the late 1950s denoting “anything that caused fear and/or horror” (MR/413); this might be a transition towards later √RUK “terrible shapes and the fear they inspire”.
√RUN “rub, grind, smooth, polish; [ᴹ√] flat of hand or sole of foot”
A root appearing in an undated note from around 1968 as part of an explanation for the tree-name S. lebethron, given as {√RON >>} √RUN “rub, grind, smooth, polish”, with a derivatives Q. runda “smooth, polished” and [deleted] ron “smoothed by polishing”, probably Sindarin (PE17/89).
The Etymologies of the 1930s instead had the root ᴹ√RUN “flat of hand or sole of foot” with derivatives like ᴹQ. runya/N. rhein “footprint”, and also as the basis for the final element of ᴹQ. tallune/N. tellen “sole of foot” (Ety/RUN). It’s conceivable the two iterations of the root are related based on the “smoothness” of the hand or foot.
√RUS “brownish red; [ᴹ√] flash, glitter of metal”
The root ᴹ√RUS “flash, glitter of metal” appeared in The Etymologies of the 1930s with derivatives ᴹQ. russe “corruscation, †sword-blade” and N. †rhoss “polished metal” where it served as the basis for the second element of the name Maidhros “Pale-glitter” or (Anglicanized) Maidros (Ety/RUS; MAD). In The Shibboleth of Fëanor from 1968, the second element of the names S. Maedros and S. Amros were explained as S. ross < ✶russā referring to their red-brown hair (PM/353, 366; VT41/10). A related etymological note stated:
Common Eldarin (u)rus [was] used of a varying brownish red from what we should call brick-red to auburn. Hence Quenya, Telerin urus (stem urust-), Sindarin rust “copper”, rustui adj.; Quenya {ruska “red-brown”} rusko “a fox” (rusku-, pl. rusqui; ruskuite “foxy”). (calarus(t)- polished copper, lairus(t) verdigris). russe a head or pelt of red hair, russa red-haired. S. rusc fox, ross ([primitive] russā) red-haired, copper coloured, especially used of animals, as fox, red deer, and [?similar kind] (VT41/10).
This use of √(U)RUS as brownish-red is not entirely without precedent: in The Etymologies of the 1930s Tolkien gave the “root” (more likely just a primitive form) ᴹ√RUSKĀ with derivative N. rhosc “brown” (Ety/RUSKĀ), the basis for the name N. Rhosgobel “Brownhay” from Lord of the Ring drafts from the 1940s (TI/164), later translated as “russet village or ‘town’ (enclosure)” (RC/241). However in notes also associated with The Shibboleth of Fëanor, Tolkien gave the root √URUN = “copper” apparently as an extension of √RUN “red, glowing”, part of an explanation of the sobriquet of Nerdanel’s father: Q. Urundil “Copper-lover” (PM/366).
Neo-Eldarin: For purposes of Neo-Eldarin, I think it best to assume 1930s ᴹ√RUS “flash, glitter of metal” was discarded in favor of 1968 √RUS “brownish red”. I’d also use √RUS as the basis for copper words rather than √URUN.
√RUTH “anger, rage, wrath”
This root appeared in two different documents: first in Quenya Notes (QN) from 1957 as (U)RUÞ “anger, rage, wrath” (PE17/188), and again in notes on Dalath Dirnen (DD) from 1964 as RUTH “rage” (PE17/183). In the former it had derivatives like Q. rúsë “anger”/S. rûth “rage” and Q. ursa “rage”/S. oroth “rage, anger”, with the latter document only mentioning the Sindarin forms with glosses “wrath” and “rage” respectively.
It’s conceivable this late root is a reemergence of a (hypothetical) root *ᴱ√(G)RUYU that would explain words in the Gnomish Lexicon of the 1910s such as G. grui “ferocity, horror”, G. gru(i)m “fierce”, and G. gruith “deed of horror, angry or violent act, vengeance” (GL/42), but it is hard to be sure.
ᴱ√RU’U “?”
An unglossed root in the Qenya Lexicon of the 1910s, probably actually *ᴱ√RUƷU, with derivatives like ᴱQ. rú “dwelling, village, hamlet”, ᴱQ. rue “rest, stillness, remaining, steadfastness”, and ᴱQ. ruin “peace” (QL/80). There were a number of likely-related words in the contemporaneous Gnomish Lexicon such as G. rô “enduring, long suffering; quiet, gentle, docile”, G. rû “dwelling, house”, and G. rûtha- “dwell, remain”, though Tolkien seems to have rejected the Gnomish forms beginning with rô- (GL/66). There are no signs of this root in Tolkien’s later writing, but I think it is worth positing a Neo-Root ᴺ√RUH “*still” to preserve some of these early words.
√RUY “blaze (red)”; √RUN “red, glowing”; ᴹ√ROY² “ruddy, red”
The root ᴹ√ROY² “ruddy, red” appeared in The Etymologies of the 1930s with Noldorin variant ᴹ√GROJ and derivatives ᴹQ. roina/N. gruin “ruddy” (Ety/ROY²). The latter seems to be an element in the names N. Dunruin “Red Valley” and N. Ruinnel “Redway” from Lord of the Rings drafts from the 1940s (RS/464; TI/114). These names eventually became S. Nanduhirion “Dimrill Dale” and S. Celebrant “Silverlode” (LotR/283; LotR/341).
A similar root √RUYU “blaze (red)” appeared in 1964 notes on Dalath Dirnen (DD), with derivatives like Q. ruinë “fire, blaze” and Q. ruimen/S. ruist “fireplace, hearth”. In this note Tolkien contrasted Q. ruine “fire, blaze” with nār- “fire as an element”. The note seems to be inspired by a proposed alternate name S. Angruin “Iron Fire” for S. Glaurung; this alternate name was rejected with an “X”, but the rest of the note was allowed to stand. It’s probable the element -ruin is the same one seen in S. Orodruin “Mountain of Fire” (LotR/899), a name that dates back to Lord of the Rings drafts from the 1940s.
The word ruin in turn was connected to the root √RUN “red, glowing” in notes associated with The Shibboleth of Fëanor from 1968, having derivatives Q. runya/S. ruin “fiery red” (PM/365-6 note #61). Thus we tentatively have the conceptual development: 1930s ᴹ√ROY² “ruddy, red” >> 1964 √RUY “blaze (red)” >> 1968 √RUN “red, glowing”.
Neo-Eldarin: For purposes of Neo-Eldarin, I’d stick with 1964 √RUY “blaze (red)” as the version of the root having the largest and must useful set of derivatives.