Source : Webster's Revised Unabridged Dictionary (1913)

Decisive \De*ci*sive\, a. [Cf. F. d['e]cisif. See {Decision}.]
   1. Having the power or quality of deciding a question or
      controversy; putting an end to contest or controversy;
      final; conclusive. ``A decisive, irrevocable doom.''
      --Bates. ``Decisive campaign.'' --Macaulay. ``Decisive
      proof.'' --Hallam.

   2. Marked by promptness and decision.

            A noble instance of this attribute of the decisive
            character.                            --J. Foster.

   Syn: Decided; positive; conclusive. See {Decided}. --
        {De*ci"sive*ly}, adv. -- {De*ci"sive*ness}, n.

Source : WordNet®

decisiveness
     n 1: the trait of resoluteness as evidenced by firmness of
          character or purpose; "a man of unusual decisiveness"
          [syn: {decision}] [ant: {indecisiveness}, {indecisiveness}]
     2: the quality of being final or definitely settled; "the
        finality of death" [syn: {finality}, {conclusiveness}]
        [ant: {inconclusiveness}]