√N(D)IL “to love (as a friend or equal), be devoted to; [ᴹ√] love, devotion; friend”
This root for friendship and devotion first appeared as ᴹ√NIL or strengthened ᴹ√NDIL “friend” in The Etymologies of the 1930s with a number of Quenya derivatives of similar meaning, the most significant being the suffixes ᴹQ. -nil or -dil, which Tolkien said was the equivalent of Old English “-wine” (“-friend”). In The Etymologies, ᴹ√DIL was an unrelated root meaning “stop up, fill up hole” (Ety/DIL). The strengthened root ᴹ√NDIL was mentioned again with the gloss “love, devotion” in The Notion Club Papers of the 1940s (SD/241, 305).
The unstrengthened form √NIL appeared in a letter to David Masson from 1955, where Tolkien said “√NIL means to love as a friend or equal”, as opposed to √(N)DUR which meant “to show special interest in things such as trees, astronomy, gems, medicine, sea, etc.” (PE17/152). Tolkien went on to say that, properly speaking, -(n)dil could apply only to persons and -(n)dur should be used of things, with names like Meneldil and Anardil being “Mannish” misuses of the suffix.
The root appeared again as √(N)DIL “to love, be devoted to” in the draft of a letter to Mr. Rang from 1967, where Tolkien clarified that it described “the attitude of one to a person, thing, course or occupation to which one is devoted for its own sake” (Let/386). This seems to be the only place where Tolkien clearly indicates the unstrengthened form is √DIL. Tolkien again clarified the distinction with √(N)DUR in a footnote:
This provides the key to a large number of other Elvish Q. names, such as Elendil “Elf-friend” (eled+ndil), Valandil, Mardil the Good Steward (devoted to the House, sc. of the Kings) Meneldil “astronomer” etc. Of similar significance in names is -(n)dur, though properly this means “to serve”, as one serves a legitimate master: cf. Q. arandil “king’s friend, royalist”, beside arandur “king’s servant, minister”. But these often coincide: e.g. Sam’s relation to Frodo can be viewed either as in status -ndur, in spirit -ndil. Compare among the variant names: Eärendur “(professional) mariner” (Let/386).
Neo-Eldarin: For purposes of Neo-Eldarin I would leave the unstrengthened form of this root as √NIL to retain the use of ᴹ√DIL “stop up, fill up hole” from the 1930s. I would also assume that √N(D)IL means “devotion” from a position of equality and friendship, as opposed to √(N)DUR which means devotion from a position of subservience. Hence Elendil = “Elf friend” [as equals] but Valandur = “Servant of the Vala” [from a lesser position].
A root appearing as √(N)DIP/B “bending and drooping” in notes probably from around 1959 given as an influence on S. nimp “pale, pallid”, and as a variant of √(N)DUB of similar meaning (PE17/168). Its Quenya derivatives Q. nimpa “drooping” and Q. limpa “frail” indicate both the strengthened and unstrengthened forms were in use. Based on the derived forms, probably √(N)DIP meant “droop” vs. √(N)DUB = “bend”.
An unglossed root in The Etymologies of the 1930s with derivatives like ᴹQ. nóla “round head, knoll” and N. dôl “head” (Ety/NDOL), the latter appearing in a large number of Noldorin and Sindarin names for hills. In the 1910s, the words ᴱQ. nóla “head, hill” and G. nôl “head” were derived from ᴱ√NOHO “extend”, making this the conceptual precursor to ᴹ√NDOL (QL/67; GL/61). On the other hand, in the 1910s the root ᴱ√NDOLO meant “delve” with derivatives like ᴱQ. noldare/G. doldrin “mole” and ᴱQ. nolmo/G. dolm “pit” (QL/65; GL/30). As for the later form of the root, the soft-mutated form -dhol in S. Fanuidhol “Cloudyhead” indicates the root might have become unstrengthened √DOL, or at least had an unstrengthened variant.
√NDOR “land; hard, firm; [ᴹ√] dwell, stay, rest, abide”
This root was the basis for “land” words for much of Tolkien’s life. It first appeared in a deleted note from the Qenya Lexicon of the 1910s: “Nōre, -nor land is different from family, one = Gnome Dor, other Gor. NᵈOR and NGOR”; the editors indicate that the superscript “ᵈ” was a later addition (QL/67). The Poetic and Mythological Words of Eldarissa also mention nᵈor and ŋor as the basis for ᴱQ. nóre (PE12/66, 67). However in the Qenya Lexicon proper, ᴱQ. nóre “native land, nation, family, country” was given under the root ᴱ√NŌ “become, be born” with variant ᴱ√NDO; the root was originally given as ŊŌ (QL/66). Thus it seems the two roots NDO(R) and ŊO(R) were combined. In the contemporaneous Gnomish Lexicon, G. dôr “land, country (inhabited), people of the land” appeared, probably from NDO(R) (GL/30), whereas “family, kinship” was nothri instead, almost certainly from ᴱ√NŌ given its relationship to G. nost “birth” (GL/61).
The two roots were separated again in The Etymologies of the 1930s where the root ᴹ√NDOR “dwell, stay, rest, abide” was the proper basis for “land” words, but in Quenya was blended with nóre “clan, race” from the root ᴹ√NŌ “beget” (Ety/NDOR, NŌ). This derivation allowed Tolkien to retain his preferred suffixes Q. -nóre/-nor vs. N./S. -dor for “-land”, and he mentioned this parallel derivation several times in later writings (PE17/26, 106-107; WJ/413 note #25). The only later change was in the gradual refinement of the meaning of NDOR as more properly referring to (dry) land as opposed to water, seas and swamps (PE17/106, 181), properly a strengthened form of √DOR “hard, tough” (PE17/181; WJ/413).
A root appearing as √(N)DUP/B “bending and drooping” in notes probably from around 1959 given as the basis for Q. lúva “bend, bow, curve” and Q. numba “bent, humped”, so most likely meaning “bend” as opposed to √(N)DIP/B = “droop”, another root appearing in the same note; the pair was glossed “bending and drooping” (PE17/168). In another set of notes written between the first and second edition of The Lord of the Rings, Q. lúva “bow, bight” was derived from √LUB “bend” (PE17/122). Yet another probably related primitive form is ✶luʒu > ✶lū in a discussion of monoconsonantal primitive roots from 1968; one of the derivatives of ✶luʒu was Q. luhta- “to bow” (VT47/35). Of the three, I prefer √(N)DUB as the basis for Q. lúva for purposes of Neo-Eldarin, as it has the greatest set of derivatives and related forms.
ᴹ√(N)DUL “hide, conceal”
A root in The Etymologies of the 1930s given as ᴹ√DUL “hide, conceal” with a strengthened variant ᴹ√NDUL and derivatives like ᴹQ. nulla/N. doll “secret; dark, dusky, obscure” as well as N. delia- “conceal” with past participle N. dolen “hidden, secret” (Ety/DUL, NDUL). This root contributes to one of the meanings of N. Gondolin = “(Heart of) Hidden Rock” = N. gonn + dolen or N. gonn + doll + N. ind “heart” (EtyAC/GOND; Ety/DUL). Tolkien’s continued use of “Hidden Rock” as one of the translations of Gondolin in later writings indicates the ongoing validatity of the root √(N)DUL:
Or so its name [Hidden Rock] was afterwards known and interpreted; but its ancient form and meaning are in doubt. It is said that the name was given first in Quenya (for that language was spoken in Turgon’s house), and was Ondolindë, the Rock of the Music of Water, for there were fountains upon the hill. But the people (who spoke only the Sindarin tongue) altered this name to Gondolin and interpreted [it] to mean Hidden Rock: Gond dolen in their own speech (WJ/201).
√(N)DUR “to show special interest in things; [ᴹ√] bow down, bend (low), obey, serve; grow/be dark”
Counterpart to the root √N(D)IL, this root first appeared in a marginal note from The Etymologies of the 1930s as ᴹ√NDUR or ᴹ√DUR “bow down, bend (down), obey, serve”, an elaboration of ᴹ√NDŪ “go down, sink, set (of Sun)” (Ety/NDŪ; EtyAC/NDŪ). In the Quenya Verbal System of the 1940s, ᴹ√NDUR was glossed “grow, be dark”, no doubt in connection to N./S. dûr “dark” (PE22/103), but later this word was connected more directly to √NDU “under, down”. Indeed, in a 1955 letter to David Masson, Tolkien gave √(N)DUR an origin distinct from √N(D)U, basing it on an independent root √DUR “to show special interest in things” (PE17/152). There was also an unglossed and deleted root ᴹ√DUR in The Etymologies of the 1930s (EtyAC/DUR).
Neo-Eldarin: For purposes of Neo-Eldarin, I think it best to keep the connection between √NDUR “bow down = serve” and √NDU “descend”. As for the semantic distinctions between -(n)dil and -(n)dur, see the entry on the root √N(D)IL for details.