The word sayonara means "goodbye" or "farewell." When you are seeing your friend off at the airport, you can wave and say, "Sayonara!"
Sayonara is a casual way to say goodbye, similar to phrases like "so long" or "see ya!" You might say sayonara to your traveling grandmother, or say sayonara to a terrible job at the end of a long summer. It's a Japanese word that has been a popular informal word in English since the late 1800s. It literally means "if it is to be that way," combining sayo, "that way," and nara, "if."