Source : Webster's Revised Unabridged Dictionary (1913)

Doubtfulness \Doubt"ful*ness\, n.
   1. State of being doubtful.

   2. Uncertainty of meaning; ambiguity; indefiniteness. `` The
      doubtfulness of his expressions.'' --Locke.

   3. Uncertainty of event or issue. --Bacon.

Source : WordNet®

doubtfulness
     n 1: the state of being unsure of something [syn: {doubt}, {uncertainty},
           {incertitude}, {dubiety}, {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: {doubt},
         {dubiousness}, {question}]