Belly up is an idiomatic phrase that means to go bankrupt, fail or fail miserably. The antonyms for "belly up" include "thrive," "succeed," "prosper," "flourish," "thrive," and "grow." These terms are used to describe situations where a business or person is thriving and doing exceedingly well. Prosperity and growth are signs of success, unlike the failure which is the opposite of success. A failing business or person must strive to turn around situations and strive to become successful again. Using the appropriate antonyms will help to provide a clear and concise narrative.