From Longman Dictionary of Contemporary Englishgoodbyegood‧bye /ɡʊdˈbaɪ/ ●●●S3GOODBYEused when you are leaving someone, or when they are leaving → helloGoodbye, John, see you tomorrow.I just have to say goodbye to Jane.say your goodbyes (=say goodbye to several people or everyone)We said our goodbyes and left.THESAURUSgoodbye used when you are leaving or when someone is leaving you. Goodbyesounds rather formal and is used especially when talking to people you do not know well. In everyday English people usually just say bye‘Goodbye, Mrs Moore.’ ‘Goodbye, Dr Aziz.’Thank you for calling. Goodbye.bye goodbye‘Bye, Annie.’ ‘Bye, Mom, ’ she said, kissing her mother on the cheek.Bye everyone!Bye for now (=used especially on the phone when you will speak to someone soon) - call me if you need anything.see you informal used when saying goodbye to a friend who you will see again soonSee you, Darren.‘I’m going now.’ ‘Okay. See you tomorrow.’Safe trip back guys and we’ll see you soon.later/catch you later informal used when saying goodbye to a friend you will see again soon. These expressions sound very informal and are used especially by young peopleCatch you later, Matt. ‘Later, Mike.’ ‘Later, Steve.’see you around informal used when saying goodbye to someone and you are not sure when you will see them againHe spent the night with me and then just said ‘See you around’ and left.so long American English used when saying goodbye to someone who you will not see again for a long time‘So long, ’ he said. ‘Don’t forget to write.’She grabbed Nick by the shoulders and hugged him affectionately. ‘So long, Nick.’have a good weekend/a great trip etc used when saying goodbye to someone to wish them a good weekend, an enjoyabletrip etcHave a nice weekend.Have a great time at the concert, guys!have a nice day used by people working in shops when saying goodbye to customersHere’s your change. Have a nice day.take care used when saying goodbye to someone, especially someone you like every much, to show that you care about them‘Bye love ! Take care.’ ‘You too! Bye!’ cheerio British English informal goodbye. Cheerio sounds rather old-fashioned and is used especially by older people Right, well we’re going now, cheerio then!cheers British English informal goodbye – used especially by younger peopleCheers, mate! See you soon.