Based on Size:
* Macroorganism: This refers to an organism visible to the naked eye.
* Large organism: This is a more general term for a large organism.
Based on Complexity:
* Multicellular organism: This describes an organism composed of many cells.
* Complex organism: This emphasizes the sophisticated structure and function of an organism.
Based on Function:
* Host: This is relevant if you're discussing microorganisms as parasites.
* Larger life form: This is a broad term that encompasses all life forms bigger than microorganisms.
Example:
If you're talking about the difference between bacteria and humans, you might say "humans are macroorganisms, while bacteria are microorganisms."
Ultimately, the best antonym depends on the specific context and what you want to emphasize.