The phrase "is on par" means to be at the same level as something or someone else. Some antonyms for this term may include "below par," "substandard," "inferior," "less than," or "lacking." These antonyms suggest a lower level of performance, quality, or achievement compared to the standard or expectation. In contrast, opposites such as "above par," "outstanding," "superior," "excellent," or "exceptional" denote a higher level of excellence or surpassing the norm. Using antonyms can help clarify the intended meaning of a sentence and express a contrasting or opposite opinion.