√KHOM root. “heart”
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 from the early 1950s Tolkien wrote CE ✶khōm “heart” (PE19/102). In this same document he wrote in a marginal note:
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).
This note was written in green ball point pen which Tolkien used for revisions to this document circa 1970, so it seem the conceptual history for the forms of this root was 1910s √HON >> early 1930s √HOM >> mid 1930s-early 50s √KHON >> mid 1950s-1970 √KHOM. 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.
Reference ✧ PE19/97 ✧ khō̆m “heart”
ᴹ√KHO(N) root. “heart (physical)”
References ✧ Ety/GOR, KHŌ-N