How does a priest address another priest?
The same as anyone else, Father. if however they know each other, like anyone in similar professions, by name.
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It is considered good form among priests to address each other by the title “Father” if in public, and by name only if they are not among the faithful. Now a days, priests are so familiar many disregard the title Father and allow all to call them by their first name if not a short form or nickname.