Middle English obeien, borrowed from Anglo-French obeir, going back to Latin oboedīre, from ob- "toward, in the direction of" + -oedīre, probably unstressed form (with -oe- of uncertain origin) of audīre "to hear" — more at ob-, audible entry 1

Note: The -oe- in oboedīre is peculiar both because it is not the expected result of -au- in a non-initial syllable (the regular outcome is -ū-) and because -oe- is in any case rare non-initially. Various attempts have been made to account for the irregularity. Reflecting earlier suggestions, Michiel de Vaan hypothesizes pre-Latin *ób-awizdijō > *obowizdijō > *oboizdijō (rounding of a before w, which is then lost, prior to the weakening of a to u) > oboediō (with z blocking monophthongization of -oi- to -ū- before succumbing to cluster reduction) (see Etymological Dictionary of Latin and the Other Italic Languages, Brill, 2008). As an alternative to assumptions of questionable phonetic change, it has also been suggested that a base other than audīre is at issue (Michael Weiss suggests *ob-bhoi̯diō, from a nominal derivative of the base of fīdere "to trust" [see faith entry 1]; see Outline of the Historical and Comparative Grammar of Latin, Ann Arbor, 2009, p. 120).