The word "most aeonian" refers to something that is the most eternal or never-ending. Its antonyms can be terms like limited, temporary, fleeting, mortal, and transient. Limited refers to something that has a specific duration, while temporary denotes something that is not meant to last. Fleeting describes something that lasts for a short time, while mortal refers to something that is subject to death or decay. Transient describes something that is passing or not permanent. All of these terms are antonyms for "most aeonian" in that they imply a limited duration, a finite existence, and a sense of impermanence.