Wave a flag is a common expression that means to show support for a cause or belief. There are many synonyms for this phrase, including to advocate, champion, endorse, promote, back, encourage, espouse, further, and uphold. These words all embody the idea of actively supporting and endorsing a particular cause or belief. When you wave a flag, you are essentially saying "I stand behind this", and these synonyms capture that same sentiment in a variety of ways. Whether you're advocating for a political candidate or rallying behind a social justice movement, there are many ways to express your passion and enthusiasm for the causes you care about.