The word "belly-flops" refers to a diving or jumping maneuver where someone lands flat on their stomach. Its antonyms would be dive, jump, or plunge, where a person lands on their feet, back, or sides respectively. These words are often associated with grace and elegance, whereas belly-flops are considered clumsy and awkward. Other antonyms for belly-flops could include smoothly, successfully, and gracefully. These words imply a successful execution of a maneuver, in contrast to the negative connotations associated with belly-flops. Using appropriate antonyms can help to convey a more positive and optimistic tone in writing or conversation.