The phrase "more livelong" doesn't have a direct antonym, as it's not a commonly used expression. However, if we break down the two words separately, we can list some possible antonyms. "More" can be antonymized as "less," "fewer," or "decreased." While "livelong" could be antonymized as "dying," "short-lived," or "ephemeral." These antonyms present the opposite meaning of the original phrase, which implies that something or someone is robust, lively, and full of energy. The choice of antonym will depend on the context of the sentence, but typically the opposite of "more livelong" would signify weakness, fragility, or a brief span of life.