The word "Undoubtful" means certain, confident, or positive. Its antonym is doubtful, which means uncertain, hesitant, or suspicious. Synonyms of doubtful are unsure, dubious, or skeptical. Doubtful can be used to describe a situation or a person's beliefs or opinion. It can also be used to express uncertainty about the truth of something. Doubtful is an expression of skepticism or a lack of belief. In contrast, undoubtful expresses a strong conviction or belief in something, while doubtful expresses a lack of certainty or confidence. Using the correct antonym can make a significant difference in the meaning conveyed.