papa

Papa, papae, first declension but masculine, like nauta, poeta and agricola: the ending is feminine, the agreement is not, so papa sanctus and not papa sancta.

It begins as a child's word for father, the same nursery syllable as in most European languages, and becomes a warm title for any bishop. In the Greek East it still is one, which is why an ordinary Orthodox parish priest is a papas. Only from the fifth century does the Latin West start reserving it for the bishop of Rome, and Gregory VII made that exclusive by decree in 1075. The corpus spelling pape for papae is medieval: ae had collapsed to a plain e in speech, and scribes wrote what they heard.