ᴱ√MEHE “(?)ooze, *gore”
A root in the Qenya Lexicon of the 1910s glossed “ooze”, but Tolkien marked that gloss with a “?”, and its Qenya and Gnomish derivatives all had to do with “gore”: ᴱQ. mear, G. †mais, and G. mechor (QL/60; GL/56-57). There are no signs of this root in Tolkien’s later writing, but I think it is worth positing a Neo-Eldarin root ᴺ√MEKH for “gore” words.
ᴱ√MEKE “*centre; aim”
An unglossed root in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. mekta “center”, ᴱQ. mekte- “aim at”, ᴱQ. meqa “middle”, and ᴱQ. met (mekt-) “mark, aim, object” (QL/60). In the contemporaneous Gnomish Lexicon it had derivatives like G. mectha “goal, intention” and G. mectha- “aim at; intend, mean” (GL/57). Words for “middle” were derived from √ENED in Tolkien’s later writings, but I think it is worth retaining a Neo-Eldarin root ᴺ√MEK “aim” to salvage other early “aim” and “goal” words derived from this root.
√MEL “love, [ᴹ√] love (as friend)”
This root was the basis for Elvish “love” words for all of Tolkien’s life, but it is unclear whether it was as general as the English word for “love” or if it was more limited to [Greek] “philia”, non-romantic love between friends. The root first appeared as ᴱ√MELE “love” in the Qenya Lexicon of the 1910s with derivatives like ᴱQ. mel- “to love”, ᴱQ. meles(se) “love”, and ᴱQ. melin “dear, beloved” (QL/60). In the contemporaneous Gnomish Lexicon it had similar derivatives like G. mel- “love” and G. melon “dear, beloved” (GL/57).
In The Etymologies of the 1930s Tolkien specified that ᴹ√MEL meant “love (as friend)”, and for the first time it included the derivative N. mellon “friend” (Ety/MEL); Gnomish “friend” words from the 1910s were mostly based on G. ged (GL/38). However, the same entry included ᴹQ. melindo/ᴹQ. melisse “lover” (male and female), so it seems even in the 1930s it could refer to romantic love (Ety/MEL). The root continued to appear in Tolkien’s later writings associated with “love” (PE18/46, 96; PE17/41; VT39/10).
For purposes of Neo-Eldarin, I would assume that like English √MEL can be used for both romantic and non-romantic love, but that the Elves were more inclined to use such words with friends as well as lovers, and did not attach the same romantic weight to “I love you” that English speakers do.
√MEN “go, move, proceed (in any direction); make for, go towards; have as object, (in)tend; direction, object, point moved toward”
This root first appeared as unglossed ᴹ√MEN in The Etymologies of the 1930s, but seemed to be more stationary in nature given its derivatives ᴹQ. men “place, spot” and ᴹQ. ména “region” (Ety/MEN). It was an element in direction words like ᴹQ. formen/N. forven, apparently meaning “*north place” as this conceptual stage. In the Quenya Verbal System of the 1940s, Tolkien first gave the root the gloss “aim at, intend, purpose” with the more specific sense “make for, proceed towards” when used with the allative, but then crossed this out and simply made the gloss “go, proceed” (PE22/103 and note #21). In Common Eldarin: Noun Structure of the early 1950s, Tolkien first gave √MEN the gloss as “place, situation, site”, then revised it to “direction, object, point moved toward” (PE21/79 and note #39).
Thereafter Tolkien mostly gave this root the basic sense “go” (PE17/93, 143, 165; VT39/11; VT42/32). Tolkien gave a somewhat lengthy description of the root in Definitive Linguistic Notes (DLN) from 1959:
√MEN go, move, proceed in any direction (irrespective of speaker’s position, or assumed point of thought). mēn- a way, a going, a mov[ement] (PE17/165).
Thus in the 1950s and 1960s, Q. formen likely meant “*north way” rather than “*north place”. Unfortunately, the suffix -men is often used as “-place” in Elvish neologisms, especially older ones. I recommend against that use, and suggest using *√NOM for that purpose instead, as in Q. nómë “place”. I also sometimes see √MEN use for movement in general (as in motion picture) rather than movement in a direction. I personally recommend using ᴱQ. lev- “(intr.) move” from Qenya Wordlists of the 1920s for that purpose (PE16/132) since I think it is important to distinguish “move” from “go”, but if you prefer to use only later words you might be more comfortable expanding the semantic scope of √MEN to movement in general.
√MENEL “heavens, firmament, [ᴹ√] sky”
This root was first mentioned in notes on the Adûnaic language from the 1940s with the meaning “heavens, sky” (SD/414), and √MENEL appeared in Common Eldarin: Noun Structure from the early 1950s with the gloss “heavens, firmament” (PE21/84). Both Q. and S. menel appear quite regularly in Tolkien’s writings from the 1940s forward.
√MER “wish (for), want, desire”
In The Etymologies of the 1930s there were two roots: unstrengthened ᴹ√MER “wish, desire, want” and strengthened ᴹ√MBER, unglossed but with derivatives like ᴹQ. meren(de)/N. bereth “feast, festival” and ᴹQ. merya/N. beren “festive, gay, joyous” (Ety/MBER, MER). It is not clear whether Tolkien intended these roots to be related; the entry for ᴹ√MBER first gave the root as ᴹ√MER with N. mereth and meren, only to change it to ᴹ√MBER, N. bereth and beren when ᴹ√MER “wish, desire, want” was introduced (Ety/MBER; EtyAC/MBER).
In both earlier and contemporaneous Silmarillion drafts of the 1930s, however, Tolkien used N. Mereth Aderthad for “Feast of Reuniting” (SM/329; LR/126, 253) and continued to use S. Mereth Aderthad in the Silmarillion narratives of the 1950s and 60s (S/113; WJ/34). Possibly also related was the revision of the name Beril “Rose” to S. Meril in the unpublished epilogue to The Lord of the Ring written from the end of the 1940s (SD/117; SD/126). Conversely, {√MED >>} √MER “wish for, want” appeared in the Quenya Verbal System of the 1940s (PE22/102; 103 note #23) and Q. mer- “hope” appeared in the so-called “Merin Sentence”: Q. merin sa haryalyë alassë nó vanyalyë Ambarello “I hope that you have happiness before you pass from the world”, of unknown date but certainly written after the 1st edition of The Lord of the Rings (MS).
Thus it seems Tolkien merged ᴹ√MBER back into ᴹ√MER, though the meaning of the combined root isn’t clear given its various derivatives with senses like “feast”, “rose” and “wish, hope”. The last of these probably remained the core meaning, perhaps with “festive” extrapolated from “hopeful”.
√MET “end, finally”
This root first appeared as ᴹ√MET “end” in The Etymologies of the 1930s (Ety/MET). It may have had a conceptual precursor in ᴱQ. met “mark, aim, object”, but that word was derived from ᴱ√MEKE and had a stem form mekt- (QL/60). In any case, met- appeared quite frequently for “end” words from the 1930s forward, and the root itself was mentioned in a list from the late 1950s or early 1960s where Tolkien clarified that it had to do with “finally” only, as opposed to √TEN which meant “end” in the sense “point aimed at” (VT49/24).