doubt

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To be undecided or skeptical about: began to doubt some accepted doctrines.
2. v. To tend to disbelieve; distrust: doubts politicians when they make sweeping statements.
3. v. To regard as unlikely: I doubt that we'll arrive on time.
4. v. Archaic To suspect; fear.
5. v. To be undecided or skeptical.
6. n. A lack of certainty that often leads to irresolution. See Synonyms at uncertainty.
7. n. A lack of trust.
8. n. A point about which one is uncertain or skeptical: reassured me by answering my doubts.
9. n. The condition of being unsettled or unresolved: an outcome still in doubt.
10. idiom. beyond Without question; certainly; definitely.
11. idiom. no doubt Certainly.
12. idiom. no doubt Probably.

Century Dictionary and Cyclopedia

1. To be uncertain as to a truth or fact; be undetermined or undecided; waver or fluctuate in opinion; hesitate.
2. To be in fear; be afraid.
3. To be uncertain as to the truth or fact of; hold in question; question; hesitate to believe: as, to doubt the truth of a story.
4. To be expectant or apprehensive of; believe hesitatingly or indefinitely.
5. To distrust; be uncertain with regard to; be distrustful of: as, to doubt one's ability to execute a task.
6. To fear; be afraid of.
7. To cause to fear; put in fear; appal; daunt.
8. n. Uncertainty with regard to the truth of a given proposition or assertion; suspense of judgment arising from defect of evidence or of inclination; an unsettled state of opinion; indecision of belief.
9. n. A matter of uncertainty; an undecided case or proposition; a ground of hesitation.
10. n. A difficulty suggested or proposed for solution; an objection.
11. n. Difficulty; danger.
12. n. Hesitating apprehension; fear; dread.
13. n. Synonyms Indecision, irresolution, suspense, hesitation, hesitancy, misgiving, distrust, mistrust.
14. n. A redoubt.

Wiktionary

1. v. To lack confidence in; to disbelieve, question, or suspect.
2. v. archaic To fear; to suspect.
3. n. Uncertainty, disbelief.

GNU Webster's 1913

1. v. To waver in opinion or judgment; to be in uncertainty as to belief respecting anything; to hesitate in belief; to be undecided as to the truth of the negative or the affirmative proposition; to b e undetermined.
2. v. obsolete To suspect; to fear; to be apprehensive.
3. v. To question or hold questionable; to withhold assent to; to hesitate to believe, or to be inclined not to believe; to withhold confidence from; to distrust.
4. v. obsolete To suspect; to fear; to be apprehensive of.
5. v. obsolete To fill with fear; to affright.
6. n. A fluctuation of mind arising from defect of knowledge or evidence; uncertainty of judgment or mind; unsettled state of opinion concerning the reality of an event, or the truth of an assertion, etc.; hesitation.
7. n. Uncertainty of condition.
8. n. obsolete Suspicion; fear; apprehension; dread.
9. n. Difficulty expressed or urged for solution; point unsettled; objection.

WordNet 3.0

1. v. lack confidence in or have doubts about
2. v. consider unlikely or have doubts about
3. n. the state of being unsure of something
4. n. uncertainty about the truth or factuality or existence of something