A root appearing in etymological notes from around 1964 (DD) glossed “narrow, thin” along with a set of Quenya derivatives of similar meaning (PE17/166).
Primitive elvish
thin
root. *grey
thindi
adjective. grey
thindā
adjective. grey
thini
adjective. grey
stin
root. grey
nakh
root. narrow, thin
spini-
noun. thin thread
dene
adjective. thin and strong, pliant, lithe
si
root. this, this, [ᴹ√] here, now
Tolkien used √SI as the basis for “near demonstratives” like “here” and “now” from very early in his writings on Elvish. The Qenya Lexicon of the 1910s had two competing roots ᴱ√HYA “this by us” with derivatives like ᴱQ. hyá “here by us” (QL/41) and ᴱ√KI “this by me” with derivative ᴱQ. tyá (< ᴱ✶kı̯-ā) “now” (QL/41, 49). Indications of the latter can be seen words in the contemporaneous Gnomish Lexicon such as G. cî {“now” >>} “here” and G. cîrin “present (place or time), modern” [gloss deleted] (GL/26). However, Tolkien also introduced a new root ᴱ√si(n) “this here by me” with derivatives like G. sî “here” and G. sith “hither” (GL/68). Revisions of Gnomish ci- word glosses indicate Tolkien was vacillating on which forms were temporal and which were spatial.
In The Etymologies Tolkien gave the root ᴹ√SI “this, here, now” with derivatives like ᴹQ. sí or sin “now” and ᴹQ. sinya/N. sein “new” (Ety/SI). The root √SI was mentioned a couple times in Tolkien’s later writings, usually glossed “this” (PE17/67; VT48/25; VT49/18) and in one place with the variant √SIN (PE17/67). This root was not entirely without competition in Tolkien’s later notes, however: in one place he gave primitive ✶khĭn- as the possible basis for Q. hí “here” and S. hí “now” in 1968 notes on demonstratives, though it appeared beside primitive ✶si- forms (VT49/34 note #21).
sin
root. this
sinā
adjective. this
nek
root. narrow, narrow; *angular, sharp
A root appearing in notes on words and phrases from The Lord of the Rings from the late 1950s or early 1960s, serving mainly as the basis for S. naith “angle” (PE17/55). It was also mentioned in a discussion of the death of Isildur at the Gladden Fields, again as the basis for S. naith among other words, where the root √NEK was glossed “narrow” (UT/281-2, note #16). In The Etymologies of the 1930s, N. naith was derived from ᴹ√SNAS or ᴹ√SNAT, but the precise derivation was unclear, and in any cases seems to have been replaced by Tolkien with a more straightforward derivation from √NEK.
The root √NEK also appeared in Quenya Notes (QN) from 1957 with the gloss “deprive”, serving among other things as the basis for S. neithan “one deprived” (PE17/167), which was the name adopted by Túrin after he became an outlaw (S/200). The root appeared again in notes on Elvish numbers from the late 1960s glossed as either “divide, part, separate” (VT47/16) or “divide, separate” (VT48/9), where it served as the basis for √ENEK “six” as the dividing point between the lower and upper set of numbers in the Elvish duodecimal system.
It is not clear whether Tolkien intended all these various meanings for the root √NEK to be connected. For purposes of analysis, I’ve split √NEK “narrow” from √NEK “separate; deprive”, but conceivably the sense “narrow” could be a semantic extension of “separate” or vice-versa.
mith
root. grey
Tolkien introduced the root ᴹ√MITH in The Etymologies of the 1930s as a blending of ᴹ√MIS “✱wet” and ᴹ√KHITH “mist, fog”, with the derivative N. mith “white fog, wet mist” as in N. Mithrim “✱Mist Lake” (Ety/MITH, RINGI; EtyAC/MITH). As a later addition to this entry Tolkien wrote the adjective N. mith “grey”, and that was the more common use of this word in Tolkien’s later writings. In a 1955 letter to David Masson Tolkien specified that “usage suggests that MIÞ- is paler and whiter, a luminous grey” (PE17/72).
mītha
adjective. *grey
ʒandā
adjective. long
Tolkien introduced the (unglossed) root ᴹ√THIN in The Etymologies of the 1930s with derivatives like ᴹQ. sinde/N. thinn “grey, pale” and ᴹQ. sinta-/N. †thinna- “fade” (Ety/THIN). In this document it was the basis for the name Ilk. Thingol; in earlier writings from the 1920s the name ᴱN. Thingol was based on the word ᴱN. thing “prince” (PE13/154). The root √THIN or √ΘIN was mentioned a couple times in Tolkien’s later writings as the basis for “grey” words (PE17/72; WJ/384). In a note from the mid-1960s Tolkien considered making the root √STIN the basis for “grey”, as a privative formation = √S-TIN = “without sparkling” (PE17/184), but I think this was a transient idea.