Definition of "doubtful"

doubtful

/ˈdaʊtfəl/

adjective
comparative more doubtful, superlative most doubtful
1. Subject to, or causing doubt.
2. Experiencing or showing doubt, skeptical.
3. Undecided or of uncertain outcome.
4. (obsolete) Fearsome, dreadful.
5. Improbable or unlikely.
6. Suspicious, or of dubious character.
7. Unclear or unreliable.
  Quotations
  The pupils of her great eyes were large in the doubtful lamplight, swallowing their green fires in deep pools of mystery and darkness.
  1922, E.R. Eddison, The Worm Ouroboros
noun
plural doubtfuls
1. A doubtful person or thing.
  Quotations
  They had their lists of Liberals and of the doubtfuls who still remained doubtful. As the election drew near, the force of the whole organization was turned upon these unrepentant doubtfuls.
  1976, Kenneth Gibbons, Donald Cameron Rowat, Political Corruption in Canada: Cases, Causes and Cures, page 45