The most general Quenya word for “house” or small building derived from √KAW “shelter” (PE17/107; VT47/35; WJ/369). As Tolkien described it in notes from the late 1960s:
> From √KAW was made the simple primitive form ✱kawā > Q koa, applied to any “shelter” (contrived and not natural) temporary or in Aman more often permanent, and applied to what we might call outhouses, huts, sheds, booths (PE17/108).
In another note from this period:
> As the simple name of a building used for a dwelling or other purposes Quenya used koa, a derivative of √KAW “shelter” (PE17/165).
Thus coa could be used for a “house” as a dwelling place but also for other kinds of small buildings. For an inhabited dwelling, Q. mar(da) might be more appropriate.
In some places Tolkien use coa to refer (metaphorically) to a body, as in cöacalina “light of the house” referring to a spirit within a body (MR/250), as well as the phrase: Valar ar Maiar fantaner nassentar fanainen ve quenderinwe koar al larmar “Valar and Maiar cloaked their true-being in fanar [veils], like to Elvish bodies [koar = houses] and raiment” (PE17/175).
coa ("köa")noun "house" (VT47:35, with etymology); coarya "his house" (WJ:369), allative coaryanna ("k") "to/at his house" (VT49:23, 35), quenderinwë coar ("koar") "Elvish bodies" (PE17:175). Notice how coa "house" is here used metaphorically = "body", as also in the compound coacalina "light of the house"(a metaphor for the soul [fëa] dwelling inside the body [hroa]) (MR:250)