The phrase "big idea" refers to a significant or innovative concept or plan. There are various synonyms that could be used to express similar ideas, including "grand vision," "revolutionary notion," "bold concept," "game-changing idea," "transformational thought," "epochal proposal," and "trailblazing concept." These phrases convey the concept of an idea that could significantly impact a field, industry, or even the world. A "big idea" is often associated with creativity, innovation, and risk-taking. These synonyms are useful for communicating the power and potential of an idea and can inspire others to join in its pursuit.