This root first appeared as ᴹ√SED “rest” in The Etymologies of the 1930s with derivatives like ᴹQ. sére “rest, repose, peace” and N. sîdh “peace”, along with the name of the Valië ᴹQ. Este < ᴹ✶ezdē (Ety/SED). The root √SED “rest” along with the etymology of Este reappeared in both the Outline of Phonetic Development (OP1) from the 1930s (PE19/45) and the Outline of Phonology (OP2) from the early 1950s (PE19/92), and again in revisions to the OP2 page annotated in green-ink and thus probably from 1970 (PE19/91 and note #110).
The root √SED “rest” was mentioned a couple times in the Quenya Verbal System of the 1940s as the basis for the verb ᴹQ. ser- “rest, repose” (PE22/102, 125) and again (unglossed) in the Quendi and Eldar essay of 1959-60 as the basis for Este (WJ/403). In the sense “peace” this root had some competition, however. In the first version of the Gloria in Excelsis Deo prayer from the mid-1960s, Tolkien used Q. sívë for “peace”, revised to Q. sérë in the second version and then Q. rainë (VT44/32). The word Q. sívë “peace” reappeared in unpublished etymological notes from 1969 derived from the root √SIB “rest, quiet” (VT44/35).
Neo-Eldarin: For purpose of Neo-Eldarin, I would use √SED for the act of resting and so Q. sérë “peace” = “restfulness (personal peace)”, and would use √SIB = “quiet, *stillness, absence of activity” and so Q. sívë “peace” = “absence of activity or violence (environmental peace)”. I would use Q. rainë as “good will” in connection to √RAY “smile”.
ᴹ√SEL(D) “child; *daughter”
A root in The Etymologies of the 1930s, initially glossed “daughter” but later “child” with derivatives ᴹQ. selde, ᴹQ. seldo, ᴹQ. selda = female, male and neuter “child” (Ety/SEL-D). In Notes on Names (NN) from 1957 Tolkien gave sel-de “daughter” (PE17/170), while S. sel(l) = “daughter” appeared in both the King’s Letter from the late 1940s (SD/129) as well as the Túrin Wrapper from the 1950s (VT50/5). The diminutive form for “daughter” appeared as Q. selyë in notes from the late 1960s (VT47/10).
Neo-Eldarin: For purposes of Neo-Eldarin, I prefer √YEL for “daughter”, at least in the Quenya branch of the languages, mostly so I can still use the 1930s “child” words for other genders. I would still use S. sell for “daughter” in Sindarin, with a bit of semantic drift.
√SEN “let loose, free, let go”
A primitive form given as *sen- “let loose, free, let go” to explain the verb ✶ab(a)sene- > Q. apsen- “remit, release, forgive” from the final Quenya version of the Lord’s Prayer from the 1950s (VT43/12, 18). It is probably the basis for the (mutated) element hen in similar words in the Sindarin version of the Lord’s Prayer: S. díhena- and gohena-, as suggested by Bill Welden (VT44/22, 28-29). This primitive element *sen- appears nowhere else with this meaning, and is similar in semantic scope to the better established root √LEK.
ᴹ√SER “love, be fond of (of liking, friendship)”
A root in The Etymologies of the 1930s glossed “love, be fond of (of liking, friendship)” with derivatives like ᴹQ. serme, ᴹQ. sermo, and ᴹQ. seron, all meaning “friend” = feminine, masculine and neuter respectively (Ety/SER). Tolkien also considered given this root the form ᴹ√THER (EtyAC/SER). Tolkien compared ᴹ√SER to ᴹ√SON “love, befriend, cherish” which was “only used of persons” and had derivatives ᴹQ. sonda “dear, fond” and ᴹQ. sondo/N. thond “friend” (the latter implying a root *ᴹ√THON), but the root ᴹ√SON was rejected (EtyAC/SON). Tolkien further compared ᴹ√SER to ᴹ√MEL “love (as friend)” (EtyAC/MEL), which is a much better known basis for “love” and “friend” words in both earlier and later writings. However, Tolkien’s use of S. seron “lover” in the 1968 name S. Seron Aearon “Sea-lover” (PM/348) indicates he did not complete abandon ᴹ√SER.
Neo-Eldarin: I would retain this root for purposes of Neo-Eldarin, but would assume it applies to a less intense form of love and friendship than √MEL, more “like” than “love”.
A root in Quenya Notes (QN) from 1957 given as the basis for the “blood” words Q. serke and S. sereg as well as the flower name S. seregon “blood of stone” (PE17/184), a flower name that also appeared (untranslated) in The Silmarillion (S/203). It may replace the root ᴹ√YAR “blood” from The Etymologies of the 1930s with derivatives like ᴹQ. yár and N. iâr of the same meaning, the later an element in the surname of Túrin: N. Iarwath “Blood-stain” (Ety/YAR). In later Silmarillion drafts, it became Iarwaeth (WJ/83) and then S. Agarwaen “Blood-stained”, the form it took in the published version of The Silmarillion (S/210). The etymology of S. agar- “blood” is unclear.
Neo-Eldarin: For purposes of Neo-Eldarin, I’d stick to √SEREK = “blood”.