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.

Doubting \Doubt"ing\, a.
   That is uncertain; that distrusts or hesitates; having
   doubts. -- {Doubt"ing*ly}, adv.

Source : WordNet®

doubting
     adj : marked by or given to doubt; "a skeptical attitude"; "a
           skeptical listener" [syn: {questioning}, {skeptical}, {sceptical}]