Most surmised means a conclusion or opinion formed without definite knowledge or evidence. The antonyms for 'most surmised' would be verified, certain, established, proven, confirmed, or substantiated. When an idea, thought, or belief is proven or established, it provides a firm foundation for a clear perspective. A verified fact is not open to dispute, as it is supported by evidence or sources. Substantiated means that it is supported by evidence, proof, or data. When something is confirmed, it implies that it is an accepted truth supported by credible sources. Therefore, the antonyms of most surmised give a sense of assurance and reliability.