so long . so long {interj.}, {informal} Good-bye. — Used when you are leaving someone or he is leaving you. So long, I will be back tomorrow. Categories: add yours add yours {informal} {interj.} Source: A Dictionary of American Idioms by A. Makkai, M.T. Boatner, J.E. Gates © 2025 » In RussianTo section: S Subscribe to: American Idioms► Also consider the parent subscriptions (3)Idioms feedEnglish languageHome page and general feed Post my comment Post my comment