doubtful

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. Full of doubt; having doubt; not settled in opinion.
2. Causing doubt; dubious; ambiguous; uncertain; not distinct in character, meaning, or appearance; vague: as, a doubtful expression; a doubtful hue.
3. Admitting of or subject to doubt; not obvious, clear, or certain; questionable.
4. Of uncertain issue; precarious; shifting.
5. Of questionable or suspected character.
6. Fearful; apprehensive; suspicious.
7. Indicating doubt; disturbed by doubt.
8. In prosody, variable in quantity; capable of being pronounced or measured either as a long or as a short; common; dichronous. Synonyms Uncertain, undecided. Dubious, Equivocal, etc. (see obscure, a.); problematic, enigmatical.

Wiktionary

1. adj. Subject to, or causing doubt
2. adj. Experiencing or showing doubt, sceptical
3. adj. Undecided or of uncertain outcome
4. adj. obsolete Fearsome, dreadful.
5. adj. Improbable or unlikely
6. adj. Suspicious, or of dubious character
7. adj. Unclear or unreliable

GNU Webster's 1913

1. adj. Not settled in opinion; undetermined; wavering; hesitating in belief; also used, metaphorically, of the body when its action is affected by such a state of mind.
2. adj. Admitting of doubt; not obvious, clear, or certain; questionable; not decided; not easy to be defined, classed, or named.
3. adj. Characterized by ambiguity; dubious.
4. adj. Of uncertain issue or event.
5. adj. obsolete Fearful; apprehensive; suspicious.

WordNet 3.0

1. adj. open to doubt or suspicion
2. adj. fraught with uncertainty or doubt
3. adj. unsettled in mind or opinion