√SI “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”
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).
√SIL “shine (white or silver)”
Tolkien used the root √SIL and its variant √THIL for Elvish words for shining things for most of his life. This root first appeared in the Qenya Lexicon as unglossed ᴱ√SILI with variant ᴱ√ÞILI and derivatives like ᴱQ. Sil “Moon”, ᴱQ. sili- “gleam, glint”, ᴱQ. silik “flint”, and ᴱQ. silqe “glossy hair” (QL/83), though last of these was the result of blending with ᴱ√SḶKḶ² “rich, lush”, variant of ᴱ√SṚKṚ “fat” (QL/86). The contemporaneous Gnomish Lexicon had derivatives like G. Sil “Moon” and G. silc “flint” pointing only to ᴱ√SILI (GL/67); the only indication of variant ᴱ√ÞILI was in unglossed G. thil followed by deleted forms like G. Thil “Moon” (GL/72).
By The Etymologies of the 1930s, the variants ᴹ√SIL “shine silver” and ᴹ√THIL were better established (Ety/SIL, THIL). The variant ᴹ√SIL had derivatives like ᴹQ. silme/N. silif “moonlight, light of Silpion” and the extend form ᴹ√SÍLIP from which ᴹQ. Silpion was derived (Ety/SIL), and its most notable use from the 1930s forward was as the basis for the initial element of Q. Silmaril vs. S./N. silef as in N. Silevril (Ety/SIL; PE17/23; Let/425). The variant ᴹ√THIL had derivatives like ᴹQ. Isil/N. Ithil “Moon, (lit.) the Sheen” (Ety/THIL), forms Tolkien also retained from the 1930s forward. Tolkien mentioned both root variants √SIL and √THIL with the glosses like “shine (white or silver)” regularly in his later writings (Let/425; PE17/66; PE22/136; SA/sil).
ᴱ√SIPI “whistle, pipe”
The root ᴱ√SIPI “whistle, pipe” appeared in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. simp(in)a “pipe, flute, flageolot” and ᴱQ. sipi- “pipe” (QL/84). In the contemporaneous Gnomish Lexicon the derived forms were words like G. thibin “flute” and G. thimpa- “to play a flute or whistle”, indicating an actual root form *ᴱ√ÞIPI (GL/73). The Gnomish word G. Simfi “Wailers of the Shore” = ᴱQ. Solosimpe does hint at ᴱ√SIPI (GL/67), but I suspect it is a loan word as opposed to native Gnomish G. Thlossibrim (GL/73).
Neo-Eldarin: For purposes of Neo-Eldarin I think it is worth positing a Neo-Root ᴺ√THIP to salvage early “pipe” and “flute” words.
√SIR “flow”
The root √SIR and similar roots meant “flow” for most of Tolkien’s life. The earliest form of this root was ᴱ√SIŘI [SIÐI] “flow” in the Qenya Lexicon of the 1910s with variant sini and derived forms like ᴱQ. sindi “river” and ᴱQ. síre “stream” (QL/84). The latter word became “river” in Tolkien’s later writings, and words appearing in the contemporaneous Gnomish Lexicon like G. sîr “river” and G. siriol “flowing” (GL/67-68) rather than **sidh- indicate Tolkien very early revised the root to *ᴱ√SIRI. Indeed, the root was ᴹ√SIR “flow” in The Etymologies of the 1930s, and the root appeared with this form and essential meaning several times in Tolkien’s later writings (PE22/127, 135).
ᴱ√SIRIPI “*stalk”
The unglossed root ᴱ√SIRIP is one of the few triconsonantal roots appearing in in the Qenya Lexicon of the 1910s, where it had derivatives ᴱQ. siripta “slender stem” and ᴱQ. sirpe “stem, stalk, slender tube, etc.” (QL/84). In the contemporaneous Gnomish Lexicon it had derivatives like G. sirp “straw” (GL/68) but also G. thribin “lean” and G. thrimp “stalk” from *s(i)rip- (GL/73) since initial sr- became thr- in Gnomish.
Neo-Eldarin: I think it is worth positing a Neo-Root ᴺ√THIRIP “stalk” to salvage some of these early words. I prefer ᴺ√THIRIP over just keeping ᴱ√SIRIP unchanged because (a) it better preserves the forms of more Gnomish words and (b) helps differentiate the Neo-Root from 1930s ᴹ√SRIP “scratch” (Ety/SRIP).
ᴱ√SISI “singe, etc.”
The root ᴱ√SISI “singe, etc.” appeared in the Qenya Lexicon of the 1910s with derivatives ᴱQ. sisi- “scorch, singe, fry” and ᴱQ. sisin “parched, scorched” (QL/84). Its derivatives in the contemporaneous Gnomish Lexicon were words like G. thisin “parched, withered” and G. thith “dust” (GL/73), indicating an actual root form *ᴱ√ÞISI.
Neo-Eldarin: For purposes of Neo-Eldarin I think it is worth positing a Neo-Root ᴺ√THIS to salvage some of these early words.
ᴱ√SḶTḶ “*sift”
The unglossed root ᴱ√SḶTḶ appeared in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. silt- “sift, sort out, winnow” and ᴱQ. silta “sieve” (QL/84). Gnomish words G. thlid “sieve” and G. thlid- “to sort out, sift, sieve, discriminate” from contemporaneous Gnomish Lexicon are clearly related, and the archaic past form salti (later thlinti) confirms the root was actually ᴱ√SḶTḶ (GL/73). A last hint of this root can be seen in ᴱQ. silte “sift” < ᴱ✶sḷt- with past salsie, a verb form appearing in the Early Qenya Grammar of the 1920s (PE14/58).
Neo-Eldarin: I think it is worth positing a Neo-Root ᴺ√SILIT “sift” to salvage some of these early words.