so long so long /soʊ ˈlɔŋ/

interjection

1. () [Informal] Informal terms of departure or farewell.  ( vale [Archaic] , bye [Informal] , bye-bye [Informal] , farewell , good-by [American] , good-bye [ N. American] , goodbye , sayonara [Informal, American] , so long [Informal] , cheers [Informal, British] , chin-chin [Informal, British] , ta-ra [Informal, UK] , ta-ta [Informal, British] , toodle-oo [Informal] , toodle-pip [Informal, British] )
   Informal terms of departure or farewell.
   

noun

1. [Informal] A farewell remark  ( arrivederci , au revoir , auf wiedersehen , bye , bye-bye , cheerio [Informal, British] , good day , good-by [American] , goodby [American] , adieu , adios , good-bye [ N. American] , goodbye , sayonara [American] , so long [Informal] )
   a farewell remark
    They said their good-byes
   they said their good-byes