Opeti [unless we here deal with a very old misspelling for oseti we have to consider it a secondary derivation from opiya in Caus. sense, i e. Caus. fr. upa + i. Trenckner, Notes 77, 78 offers an etym. of ā + vapati, thus opiya would be *āvupiya, a risky conclusion, which besides being discrepant in meaning (āvapati = to distribute) necessitates der. of opiya fr. opati (*āvapati) instead of vice versā. There is no other instance of *āva being contracted to o. Trenckner then puts opiya = ūpiya in tadūpiya ("conform with this", see ta˚ Ia), which is however a direct derivation from upa = upaka, upiya, of which a superl. formation is upamā ("likeness"). Trenckner's expln. of ūpiya as der. fr. ā + vap does not fit in with its meaning] to make go into (c. loc.), to deposit, receive (syn. with osāpeti) S i.236 (SA na . . pakkhipanti) = Th 2, 283 = J v.252 (T. upeti); in which Th 2, 283 has oseti (ThA 216, with expln. of oseti = ṭhapeti on p. 219). -- aor. opi J iv.457 (ukkhipi gloss); vi.185 (= pakkhipi gloss). <-> ger. opitvā (opetvā?) J iv.457 (gloss khipetvā).

Pali-English Dictionary, TW Rhys Davids, William Stede,