Source : Webster's Revised Unabridged Dictionary (1913)

Invoke \In*voke"\, v. t. [imp. & p. p. {Invoked}; p. pr. & vb.
   n. {Invoking}.] [F. invoquer, L. invocare; pref. in- in, on +
   vocare to call, fr. vox voice. See {Voice}, and cf.
   {Invocate}.]
   To call on for aid or protection; to invite earnestly or
   solemnly; to summon; to address in prayer; to solicit or
   demand by invocation; to implore; as, to invoke the Supreme
   Being, or to invoke His and blessing.

         Go, my dread lord, to your great grandsire's tomb, . .
         . Invoke his warlike spirit.             --Shak.

Source : WordNet®

invoke
     v 1: evoke or call forth, with or as if by magic; "raise the
          specter of unemployment"; "he conjured wild birds in the
          air"; "stir a disturbance"; "call down the spirits from
          the mountain" [syn: {raise}, {conjure}, {conjure up}, {evoke},
           {stir}, {call down}, {arouse}, {bring up}, {put forward},
           {call forth}]
     2: cite as an authority; resort to; "He invoked the law that
        would save him"; "I appealed to the law of 1900"; "She
        invoked an ancient law" [syn: {appeal}]
     3: request earnestly (something from somebody); ask for aid or
        protection; "appeal to somebody for help"; "Invoke God in
        times of trouble" [syn: {appeal}]