The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         Go, my dread lord, to your great grandsire's tomb, . .
         .
         Invoke his warlike spirit.               --Shak.
   [1913 Webster]