"Am apposite" is commonly used to describe something that is relevant or appropriate to a particular situation or circumstance. Antonyms for this phrase would refer to things that are irrelevant or unsuitable. Some words that come to mind include "improper," "inappropriate," "unrelated," "irrelevant," "inapplicable," and "unsuitable." In a sentence, you could say "The suggestion was improper, as it did not address the problem at hand," or "The reference was irrelevant to the discussion we were having." Using antonyms helps to convey a clear message and differentiate between what is and is not considered "am apposite.