Source : Webster's Revised Unabridged Dictionary (1913)

Doubt \Doubt\, v. i. [imp. & p. p. {Dou?ted}; p. pr. & vb. n.
   {Doubting}.] [OE. duten, douten, OF. duter, doter, douter, F.
   douter, fr. L. dubitare; akin to dubius doubtful. See
   {Dubious}.]
   1. 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.

            Even in matters divine, concerning some things, we
            may lawfully doubt, and suspend our judgment.
                                                  --Hooker.

            To try your love and make you doubt of mine.
                                                  --Dryden.

   2. To suspect; to fear; to be apprehensive. [Obs.]

   Syn: To waver; vacillate; fluctuate; hesitate; demur;
        scruple; question.

Doubt \Doubt\, v. t.
   1. 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; as, I have heard
      the story, but I doubt the truth of it.

            To admire superior sense, and doubt their own!
                                                  --Pope.

            I doubt not that however changed, you keep So much
            of what is graceful.                  --Tennyson.

   {To doubt not but}.

            I do not doubt but I have been to blame. --Dryden.

            We doubt not now But every rub is smoothed on our
            way.                                  --Shak.

   Note: That is, we have no doubt to prevent us from believing,
         etc. (or notwithstanding all that may be said to the
         contrary) -- but having a preventive sense, after verbs
         of ``doubting'' and ``denying'' that convey a notion of
         hindrance. --E. A. Abbott.

   2. To suspect; to fear; to be apprehensive of. [Obs.]

            Edmond [was a] good man and doubted God. --R. of
                                                  Gloucester.

            I doubt some foul play.               --Shak.

            That I of doubted danger had no fear. --Spenser.

   3. To fill with fear; to affright. [Obs.]

            The virtues of the valiant Caratach More doubt me
            than all Britain.                     --Beau. & Fl.

Doubt \Doubt\, n. [OE. dute, doute, F. doute, fr. douter to
   doubt. See {Doubt}, v. i.]
   1. 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.

            Doubt is the beginning and the end of our efforts to
            know.                                 --Sir W.
                                                  Hamilton.

            Doubt, in order to be operative in requiring an
            acquittal, is not the want of perfect certainty
            (which can never exist in any question of fact) but
            a defect of proof preventing a reasonable assurance
            of quilt.                             --Wharton.

   2. Uncertainty of condition.

            Thy life shall hang in doubt before thee. --Deut.
                                                  xxviii. 66.

   3. Suspicion; fear; apprehension; dread. [Obs.]

            I stand in doubt of you.              --Gal. iv. 20.

            Nor slack her threatful hand for danger's doubt.
                                                  --Spenser.

   4. Difficulty expressed or urged for solution; point
      unsettled; objection.

            To every doubt your answer is the same. --Blackmore.

   {No doubt}, undoubtedly; without doubt.

   {Out of doubt}, beyond doubt. [Obs.] --Spenser.

   Syn: Uncertainty; hesitation; suspense; indecision;
        irresolution; distrust; suspicion; scruple; perplexity;
        ambiguity; skepticism.

Source : WordNet®

doubt
     n 1: the state of being unsure of something [syn: {uncertainty},
          {incertitude}, {dubiety}, {doubtfulness}, {dubiousness}]
          [ant: {certainty}]
     2: uncertainty about the truth or factuality of existence of
        something; "the dubiousness of his claim"; "there is no
        question about the validity of the enterprise" [syn: {dubiousness},
         {doubtfulness}, {question}]
     v 1: consider unlikely or have doubts about; "I doubt that she
          will accept his proposal of marriage"
     2: lack confidence in or have doubts about; "I doubt these
        reports"; "I suspect her true motives"; "she distrusts her
        stepmother"