While "megacosm" refers to the entire universe or a vast, complex system, antonyms to this word could include smaller, more specialized terms. For example, "microuniverse" or "microcosm" could be an antonym. Alternatively, "fragment" or "fraction" would suggest a smaller or more limited portion of a larger system, rather than the whole. Similarly, "microcosmography" could be used to describe a small, detailed perspective on a particular system, as opposed to "megacosmic." Other antonyms might include "mundane," "normal," or "routine," which would suggest a smaller or more routine existence as opposed to the grandiose connotations of "megacosm.