Being one case implies that there is only a singular instance of something. The antonyms for being one case are numerous, and they include plural, many, several, multiple, and manifold. These words suggest that there are many different cases or instances of something, rather than just one. Being one case can also imply a sense of singularity or exclusivity, while the antonyms suggest a broader, more inclusive perspective. Additionally, words such as variety, diversity, and heterogeneity are antonyms for being one case, as they suggest a range of different examples or cases, rather than a single, uniform one.