Most purported refers to something that is alleged or claimed to be true, but not necessarily proven. It can also mean something that is widely believed but not necessarily accurate. Antonyms for most purported would include words that indicate something that is proven or verified. Some of the antonyms could be: proven, substantiated, validated, attested, authenticated, confirmed, established, sworn, tested, verified. Using these antonyms can help convey a sense of certainty and truthfulness, and can be useful in situations where accuracy is important.