Old English papa (9c.), from Church Latin papa "bishop, pope" (in classical Latin, "tutor"), from Greek papas "patriarch, bishop," originally "father." Papal, papacy, later acquisitions in English, preserve the original vowel. [color=#242729][size=2][font=Georgia, "Times New Roman", Times, serif]From [/font][/size][/color][url=https://en.m.wikipedia.org/wiki/Pope_(word)][color=#601f1f][size=2][font=Georgia,
"Times New Roman", Times, serif]Wikipedia:[/font][/size][/color][/url] According to the Oxford English Dictionary, the earliest recorded use of the title "pope" in English is in an Old English translation (c. 950) of Bede's Ecclesiastical History of the English People: Þa wæs in þa tid Uitalius papa þæs apostolican seðles aldorbiscop. In Modern English: At that time, Pope Vitalian was chief bishop of the apostolic see. Given the Greek/Latin original term which was adopted also by Old English, how and when did the vowel change come about?