adj. 1. Subject to or causing doubt: a doubtful claim; doubtful prospects. 2. Experiencing or showing doubt: Doubtful that the cord would hold, we strengthened it. 3. Of uncertain outcome; undecided. 4. Raising doubts as to legitimacy, honesty, or respectability; suspicious: the candidate's doubtful past. See Usage Note at doubt. doubtful·ly adv. doubtful·ness n. |
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