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.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2022 by HarperCollins Publishers. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.