When something is not up to par, it means that it's not meeting the expected or required standards. Sometimes it's necessary to find different words to describe this situation, and there are many synonyms for "not up to par." Some possible options might include inadequate, deficient, substandard, unsatisfactory, poor, below average, below par, not satisfactory, unacceptable, disappointing, or mediocre. Each of these words conveys a slightly different shade of meaning and may be more or less appropriate depending on the context. Ultimately, the most important thing is to choose words that accurately reflect the level of quality or performance that is being described.