The Collaborative International Dictionary of English v.0.48:

Effectual \Ef*fec"tu*al\ (?; 135), a. [See Effect, n.]
   Producing, or having adequate power or force to produce, an
   intended effect; adequate; efficient; operative; decisive.
   --Shak.
   [1913 Webster]

         Effectual steps for the suppression of the rebellion.
                                                  --Macaulay.
   [1913 Webster]

   Effectual calling (Theol.), a doctrine concerning the work
      of the Holy Spirit in producing conviction of sin and
      acceptance of salvation by Christ, -- one of the five
      points of Calvinism. See Calvinism.

   Syn: Effectual, Efficacious, Effective.

   Usage: An efficacious remedy is had recourse to, and proves
          effective if it does decided good, effectual if it
          does all the good desired. --C. J. Smith.
          [1913 Webster]