So long is an expression that is often used as a farewell. It can also mean "goodbye," "see you later," or "until next time". The synonym for so long includes "adios," "farewell," "au revoir," "goodbye," "ciao," "cheerio," "so long," and more. These synonyms are often used to express parting or to indicate the end of a conversation or meeting. Using these synonyms can add variety to the conversations and helps express emotions more effectively. No matter which one of these synonyms for so long that you choose, just make sure that it is appropriate for the situation and that it properly conveys your intended message.