Source : Webster's Revised Unabridged Dictionary (1913)

Powerful \Pow"er*ful\, a.
   1. Full of power; capable of producing great effects of any
      kind; potent; mighty; efficacious; intense; as, a powerful
      man or beast; a powerful engine; a powerful argument; a
      powerful light; a powerful vessel.

            The powerful grace that lies In herbs, plants,
            stones, and their true qualities.     --Shak.

   2. (Mining) Large; capacious; -- said of veins of ore.

   Syn: Mighty; strong; potent; forcible; efficacious;
        energetic; intense. -- {Pow"er*ful*ly}, adv. --
        {Pow"er*ful*ness}, n.

Source : WordNet®

powerfulness
     n : possession of controlling influence; "the deterrent power of
         nuclear weapons"; "the power of his love saved her"; "his
         powerfulness was concealed by a gentle facade" [syn: {power}]
         [ant: {powerlessness}, {powerlessness}]