The word "more undeceivable" implies a higher level of authenticity or trustworthiness. Its antonyms, on the other hand, would suggest the opposite. Words like "deceivable," "unreliable," or "dishonest" come to mind, all of which imply a lower level of truth or reliability. Other antonyms could include "inaccurate," "untruthful," or "false," which all suggest a deviation from what is true or factual. Ultimately, the antonyms for "more undeceivable" serve to undermine or contradict its positive connotations, suggesting that something is less than trustworthy or genuine.