Undubitable means unquestionable or certain. Therefore, antonyms for this word include words that suggest doubt or uncertainty. Some of the most common antonyms for undubitable are doubtful, questionable, ambiguous, uncertain, unclear, and dubious. Doubtful means unsure or uncertain. Questionable means open to doubt or dispute. Ambiguous means having multiple interpretations or unclear meaning. Uncertain means not definite or confident. Unclear means not easy to understand or ambiguous. Dubious means hesitating or doubting. Using these antonyms in writing can be helpful to create ambiguity or doubt about the subject or topic being discussed.