This primitive form was noted in the margins and rough notes from Late Notes on Verbs from 1969, glossed “before of place” (PE22/167) and “before, ahead, in front of place” (PE22/168). Primitive or Quenya forms opo/pō “before, in front of” and pōna/ompa “forward” appear in other late notes from this period associated with the Q. Ambidexters Sentence, as part of an explanation for Q. potai “therefore” (VT49/12), though this word was eventually revised to Q. epetai (VT49/8). Quenya or primitive forms opo, po, pono, poto “in front, of place” appeared in notes from the mid-1950s (VT49/32 note #12), and as suggested by Patrick H. Wynne might be a reemergence of the early root ᴱ√POT-I “after, behind (of place)” with a reversal in its meaning (QL/75). Other similar roots in the same semantic space are √APA and √EPE.
Neo-Eldarin: Tolkien’s treatment of “before” and “after” words was wildly inconsistent, but I generally prefer ✶epe for “after (of time); before (of space)” and ✶nō for its opposite. However, I think √APA and √OPO can serve as variants of √EPE, with √OPO more specifically referring to the front of things, especially given Tolkien’s use of √OP as a root referring to the front of the (open) mouth (PE17/126).
A root associated with the mouth in late notes on speech of unclear date, given as {√OK >>} √OP described as the “opening of which the lips, or pempi, are the edges: {√ōka >>} ōpa ({√OK >>} √OP). [versus] The closed mouth, pē” (PE17/126). Tolkien’s exact intent is hard to decipher, but it seems ōpa is the opening of the mouth as opposed to the lips surrounding that opening, probably in reference to its function as one of the articulatory mechanisms for speech. Its only other derivative was Q. ūpa “dumb [mute]” < ✶ūopa, used in the phrase Q. essë úpa nas “he is dumb”. Elsewhere in Tolkien’s late writings, primitive √OPO was glossed “before, ahead, in front of place” (PE22/168), so √OP might also simply refer to the front of the (open) mouth.