I want to say good-bye to my professor but I said "salve". "Salve" is to say hi and is formal (more than "ciao"). Then she said that it was not "salve" but did not tell me how to say good-bye. So can anybody tell me how to say it please? :)
"Arrivederci" is the most appropriate form to say goodbye to someone if you're in a formal context: please note that it theoretically expresses a wish to see the person you've talked to again; if you're on the phone, you could use "A risentirci" instead.
If you're looking for something even more formal, you can use "A rivederLa".