ᴹ√STAB “*wood”
An unglossed root in The Etymologies of the 1930s with derivatives like ᴹQ. sambe “room, chamber”, N. tham “hall”, and ᴹQ. samna/N. thafn “wooden post” (Ety/STAB). It seems to be a later iteration of the unglossed root ᴱ√SAMA from the Qenya Lexicon of the 1910s with derivatives like ᴱQ. san (samb-) “hall, dwelling house” and ᴱQ. sambe “room, chamber” (QL/81). Its derivatives in the contemporaneous Gnomish Lexicon seem to be G. tham “chamber, room” and G. thambros “hall”, pointing at a true root form *ᴱ√ÞAMA (GL/72). However, there are other words like G. sam- “arrange, put together, adjust, settle, reconcile” and G. samin “arranged, settled, done” that hint at a root form ᴱ√SAMA but with a different meaning “*arrange” (GL/67). Looking forward, the later form S. sammath “chambers” in Sammath Naur “Chambers of Fire” (LotR/942) may imply a later shift back to *√SAM for this root, but that conflicts with other roots like √SAM “to have”.
ᴹ√STAK “split, insert”
A root in The Etymologies of the 1930s glossed “split, insert” with derivatives like ᴹQ. sanka/N. thanc “cleft, split” and N. nestegi “insert, stick in” (Ety/STAK). S. thanc remained an element in S. Orthanc “Forked Height” (LotR/555; UT/400), indicating the ongoing validity of this root.
ᴹ√STAL “steep”
A root in The Etymologies of the 1930s glossed “steep” with derivatives like Ilk. thall “steep, falling steeply (of river)” and Ilk. thalos “torrent”, the latter used for the river name Ilk. Thalos (Ety/STAL). Tolkien continued to use the name S. Thalos in later versions of The Silmarillion, but the name was translated nowhere else, making its continued connection to the 1930s root uncertain.
√STAL “strong”
The unglossed root ᴹ√STALAG appeared in The Etymologies of the 1930s with derivatives like N. thala “stalwart, steady, firm” and N. thalion “hero, dauntless man” (Ety/STÁLAG), the latter a sobriquet of Húrin typically translated as “Steadfast” in the narratives themselves (S/199). Similar forms appeared in Early Noldorin Word-lists from the 1920s derived from the primitive form ᴱ✶stalga (PE13/153). The root √STAL “strong” was mentioned in passing as the basis for the adjective Q. astalda in a rejected page associated with roots having to do with “large & small” words, probably from the late 1960s (PE17/115; VT47/26 note #26). The name Q. Astaldo “Valiant” appeared as a sobriquet of Tulkas in later versions of The Silmarillion (S/28), replacing the earlier name Q. Poldórëa of similar meaning (MR/146, 149; LR/206).
√STAR “[ᴹ√] stiff”
The root ᴹ√STAR “stiff” appeared in The Etymologies of the 1930s with derivatives like ᴹQ. sara/N. thâr “stiff grass” and N. tharn “sapless, stiff, rigid, withered” (Ety/STAR). It had an extended variant ᴹ√STARAN serving as the basis for Ilk. thrôn “stiff, hard” in Ilk. Belthronding (Ety/STARAN). The root √STAR reappeared unglossed in Common Eldarin: Verb Structure of the early 1950s as a verbal root to illustrate certain patterns in the formation of perfect tenses; as such it may not be a “real” appearance of the root (PE22/133).
√STEL “remain firm”
A root mentioned in etymological notes for the name S. Ecthelion, where it also served as the basis for words like Q. estel/S. estel “hope” and S. thel- “intend, mean, purpose, resolve, will” (WJ/318-319). It may have replaced unglossed ᴹ√STELEG from The Etymologies of the 1930s which likewise served as the basis for the name N. Ecthelion, but had derivatives like N. thela “point (of spear)” (Ety/STELEG). All of these were rather torturous attempts by Tolkien to preserve the early Gnomish name G. Ecthelion “Lord of the Fountain” (GL/31), which no longer fit Noldorin or Sindarin phonology, since G. ecthel “fountain” >> N./S. eithel.
√STEN “cut short, limit, confine, cramp”
A root appearing in Quenya Notes (QN) from 1957 glossed “cut short, limit, confine, cramp” with derivatives Q. senna/S. thenn “short” (PE17/185). As pointed out by Chrisropher Gilson, it was likely a later iteration of the “root” ᴹ√STINTĀ (actually a primitive word) from The Etymologies of the 1930s with gloss “short” and derivatives like ᴹQ. sinta/N. thent “short” (Ety/STINTĀ)
*√STIR “face”; ᴹ√THĒ “look (see or seem)”
The root *√STIR is implied by the names Elestirnë “Star-brow” (UT/184) and Carnistir “Red-face” (PM/353), as well as the primitive word ✶stīrē “face” (VT41/10). It is probably an s-fortification of the root TIR “watch”. It may replace the root ᴹ√THĒ “look (see or seem)” from The Etymologies of the 1930s with derivatives like N. thio “to seem” and N. thîr “look, face, expression, countenance”, the latter providing an earlier etymology for N. Cranthir “Ruddy-face” (Ety/THĒ). The original gloss of this 1930s root was “perceive, see” (EtyAC/THĒ). This deleted gloss in turn indicates that 1930s ᴹ√THĒ was itself a later iteration of 1910s ᴱ√SEHE [þeχe] from the Qenya Lexicon, which was mostly connected to eye-words but also had derivatives like ᴱQ. sehta-/G. thê- “see” (PE12/21; QL/82; GL/72); see the entry √KHEN for the later derivation of eye-words.
Neo-Eldarin: For purposes of Neo-Eldarin, I would retain 1930s ᴹ√THĒ “seem”, and assume that S. thîr “face” is a blending of √STIR and ᴹ√THĒ, which would allow us to salvage N. thia- “seem”.
√STOR “steadfast”
A root appearing Notes on Names (NN) from 1957 serving as an explanation for the element S. thorn “steadfast” in the name S. Arathorn, first appearing in a rejected page with variants √STOR and √THOR (PE17/113-114) and then later as only √THOR (PE17/113). This root may be connected to Q. torna “hard” in notes on Quenya intensive forms written between the first and second edition of The Lord of the Rings, where it was an element in Q. tornanga “hard iron”, with intensive forms aristorna, anastorna that imply derivation from √STOR (PE17/56).
Neo-Eldarin: For purposes of Neo-Eldarin, I would assume this root is √STOR to avoid conflict with ᴹ√THOR(ON), the basis for “eagle” words.
ᴹ√STUD “base, ground”
The root ᴹ√SUD “base, ground” appeared in The Etymologies of the 1930s with derivative ᴹQ. sundo “base, root, root-word” (Ety/SUD), but it was given an alternate form ᴹ√STUD with Noldorin forms like {N. sunn >>} N. thund/thonn being added to the entry (EtyAC/SUD). Tolkien’s later of use of S. thond “root” (< *stundā?) in S. Morthond “Blackroot” implies the ongoing validity of this root (LotR/1115). In The Etymologies, Tolkien’s first attempt at the basis for “root” words was a deleted entry {ᴹ√NDUM/DUM >>} ᴹ√NDUB/DUB “lay base, foundation, root; found” (EtyAC/NDUB).