A noun appearing in Outline of Phonology (OP2) as part of revisions made in 1959 or later. It had the gloss “pile, (artificial) mound” and was derived from the root √KHAB “heap up, pile up” from a primitive form ✶khabnā (PE19/91). In this word, the ancient voiced stop b became nasal m before another nasal.
Conceptual Development: In the original draft of OP2, this word was given as hahta “piled mound, heap”, but this word was deleted and the section where it appeared was rejected (PE19/92). See the entry for ᴹQ. hahta for a discussion of the earlier iteration of this word.
A root glossed “heap up, pile up” appearing in revisions written sometime after 1959 in the Outline of Phonology (OP2), where it replaced √KHAG “pile up” (PE19/91 and note #110, pp. 91-92). One notable derivative of √KHAB was S. haudh “funeral mound”, as opposed to The Etymologies of the 1930s where N. hauð “mound, grave, tomb” was derived from ᴹ√KHAG (Ety/KHAG). The root ᴹ√KHAG “pile up” also appeared in the contemporaneous Outline of Phonetic Development from the 1930s (OP1), but there its derivative was given as N. haeð “heap, piled mound” (PE19/45).
Tolkien’s revision of √KHAG “pile up” > √KHAB may have been motivated by changing conceptions of the vocalization of voiced spirants in Noldorin vs. Sindarin: see the entry on how the first in pair of voiced stops vocalized for further discussion. Compare the earlier development khagda > ✱khāda > N. hauð “mound” from The Etymologies of the 1930s to the newer development khagda > ✱khaida > haeð “fenced enclosure” derived from the newly defined root √KHAG “stake”, also appearing in these post-1959 revisions of OP2 (PE19/91). As for the roots themselves, it seems 1930s ᴹ√KHAG “pile up” >> post-1959 √KHAB “pile up”, whereas √KHAG was given the new meaning “stake”. Also note that in all of these derivations from the 1930s up through the late 1950s of S./N. haudh “(funeral) mound”, the Sindarin/Noldorin word was influenced by the root √KHAW(AD) of various meanings; see that entry for details.
As for √KHAB, it also appears to be the basis for some 1968 primitive words: ✶khābā “unleavened bread” (originally from any vegetable, later just bread from grains) and ✶khabar “a loaf or cake of bread” (NM/295), perhaps referring to the stockpiling of grains as suggested by Röandil in a Discord chat from 2021.