The word "attestable" refers to something that can be proved or verified, but what about the opposite? One antonym of attestable could be unverifiable, meaning something that cannot be verified or proven. Another antonym could be implausible, which suggests that something is unlikely or not credible. Non-credible or untrustworthy could also be used as antonyms for attestable. Additionally, hypothetical, conjectural, and speculative could be antonyms for attestable, as they imply a lack of certainty or concrete evidence. It's important to consider these antonyms when discussing the credibility of information, sources, or arguments.