√KHOM root. “heart (physical organ)”
This root has a fairly long history as the basis Elvish words for the physical heart (as opposed to metaphorical). Its earliest appearance was as ᴱ√HONO in the Qenya Lexicon of the 1910s with derivative ᴱQ. hon (hond-) “heart” (QL/40), as well as G. honn “heart” appearing in the contemporaneous Gnomish Lexicon along with the added note “not used metaphorically, for which ilf is used” (GL/49).
In the Declension of Nouns from the early 1930s, Tolkien gave the words as ᴹQ. hōn “heart” with stem-form hom-, indicating that the final consonant of the primitive form was revised to -m. However, in The Etymologies of the mid-to-late 1930s the root was ᴹ√KHŌ-N “heart (physical)” (Ety/KHŌ-N), and in Primitive Quendian Structure from 1936 it was ᴹ✶khōn “heart”, and likewise in Primitive Quendian Structure: Final Consonants (PE22/64) and Notes for Quenya Declensions (PE22/66) from the 1940s, though in the last it was revised to ᴹ✶hōn (PE22/66 note #4).
The form ✶khō-n “heart” reappeared in Common Eldarin: Noun Structure from 1951-2 (PE21/71), but in Outline of Phonology (OP2) from the early 1950s Tolkien wrote CE ✶khōm “heart” (PE19/102). In notes from 1968 he again gave ✶khom as the basis for the physical heart, though in another note written at the same time, it was ✶khōn or ✶khond (NM/176 and note #2).
In a green-ink marginal note to the Outline of Phonology (OP2), Tolkien wrote:
Cf. holmo > khomlo “from the heart” us[ed] as adverb, sincerely, (?heartily). N.B. CE khō̆m, heart, is not the physical heart, but “the interior” used of the whole range of emotions or feelings. [It] is distinct from indo (?applied) to interior reflection[?] or mind (PE19/97).
These green-ink revisions were circa 1970, so this may be the last thing Tolkien wrote on the topic. It seems the conceptual history for the forms of this root was 1910s √HON >> early 1930s √HOM >> mid 1930s-early 50s √KHON >> mid 1950s-1970 √KHOM, with a (brief?) flirtation with √KHON in 1968. The switch from physical to metaphorical heart seems to be a very late idea (1970), and I would ignore it for purposes of Neo-Eldarin.
References ✧ NM/176; PE19/97
ᴹ√KHO(N) root. “heart (physical)”
References ✧ Ety/GOR, KHŌ-N