opo prep. "before, in front of" (of spatial relationships); "after" (of time), also pó, po or pono, poto (VT49:12, VT44:36, evidently a variant of apa).
Quenya
opo
preposition. in front (of place), before; after (of time)
opo
before, in front of
opo
before, ahead, in front of
apa
on
apa (2) prep. denoting "on" with reference to contact of surfaces, especially vertical surface (in the sense in which a picture hangs on a wall). Apa is said to have this meaning in various Tolkien manuscripts (VT44:26), but apa is also used for "after" (see apa #1 above), and the two were probably never meant to coexist in a single variant of Quenya. The clash may be avoided by consistently using the variants pá, pa (q.v.) mentioned by Tolkien in the sense of apa #2. Another variant gives apa, pá "on (above but touching)" (VT49:18).
apa
preposition. after (of time)
epeni
conjunction. before, *after; before
epë
before
epë prep. "before" ("in all relations but time", VT49:32), though the word was glossed "after" when first published (VT42:32; Bill Welden, the writer of the article in question, later presented this correction in VT44:38). The preposition can indeed express "after" when used of time, since the Eldar imagined future time (time that comes after the present) as being "before" them (VT49:12, 32); epë is in this respect a variant of apa, q.v. (Cf. VT49:22.) Compare epessë, q.v. Epë "before" may also be used in comparison (PE17:56, 57), apparently in much the same way as lá #2 (q.v.) (VT42:32)
nó
before
nó (3) prep. "before" (of time, compare nóvo), "at back" (of spatial relationships). In other conceptual phases, Tolkien also let the word have the opposite meaning "after" (of time) or "in front" (of space). (VT49:32).
po
before, in front of
po, pó prep. "before, in front of" (of spatial relationships) "after" (of time), also opo or pono, poto- (VT49:12, 32, VT44:36; evidently a variant of apa)
pono
pono
pono, see po, pó
pota-
verb. pota-
pota-, see po, pó
pá
on
pá, pa (1) prep. "on" with reference to contact of surfaces, especially vertical surface (in the sense in which a picture hangs on a wall); also used = "touching, as regards, concerning" (VT44:26). Another variant gives pá (and apa) with the meaning "on (above but touching)". (2) Variants of apa "after" (VT44:36), which preposition is in one source also ascribed the first meaning here discussed. For Neo-Quenya purposes, pá and pa may be used for "on" or "concerning", whereas apa is used for "after" (see entries for apa #1 and #2), or pa may also be seen as a shorter form of apa "after", as in the phrase yéni pa yéni *"years upon years" (VT44:36)
A word appearing as opo, pō, pono, poto- “in front, of place” in notes from the mid-1950s (VT49/32) and as opo, pō “before, in front of” in notes from 1969 associated with the Ambidexters Sentence (VT49/32). In the latter notes, Tolkien said these were used to mean “after (of time)” in potai “therefore” from the first and third versions of the Ambidexters Sentence, but by the fourth and later versions this had become epetai (VT49/6-8). The root √OPO also appeared in Late Notes on Verb Structure (LVS) from 1969 with the glosses “before of place” (PE22/167 note #22) and “before, ahead, in front of place” (PE22/168).
Conceptual Development: As pointed out by Patrick Wynne (VT49/32), in Tolkien’s earliest writings ᴱQ. pote meant “after, behind (of place)” based on the early root ᴱ√POT-I (QL/72). At some point in the intervening decades (O)PO flipped from “behind” to “in front”. It thus had a form similar to epë, which likewise kept flipping between “before” and “after”.
Neo-Quenya: It is possible that opo was supplanted by epë, but I prefer to assume it was a variant used only for position in space but not time: “in front”. See also apa, another similar form that I assume is used only of time.