Hi
"παπάς" in Greek means "priest".
When we address a priest in Greek we don't say "good morning priest", but "good morning father", which is "Καλημέρα πάτερ".
"πάτερ" is vocative case of the word "πατήρ".
"πατήρ" in ancient Greek means "father".
Have a look at this answer too: how to say "reverend father"?
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.