The antonyms for the word "most bettered" could be "most worsened", "most deteriorated", "most declined", "most degenerated", or "most regressed". These words convey the opposite meaning to "most bettered", which suggests improvement or progress. Using these antonyms can signify a negative change, a reduction in quality or performance, or a setback. For instance, if someone's health condition has "most worsened", it means that their health has deteriorated or declined, making them worse off than before. To avoid confusion, it is important to use the right antonym based on the context of the sentence.