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®

decisive
     adj 1: determining or having the power to determine an outcome;
            "cast the decisive vote"; "two factors had a decisive
            influence" [ant: {indecisive}]
     2: unmistakable; "had a decisive lead in the polls"
     3: characterized by decision and firmness; "an able an decisive
        young woman"; "we needed decisive leadership"; "she gave
        him a decisive answer" [ant: {indecisive}]
     4: forming or having the nature of a turning point or crisis;
        "a critical point in the campaign"; "the critical test"
        [syn: {critical}]