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]

WordNet (r) 3.0 (2006):

invoke
    v 1: summon into action or bring into existence, often as if by
         magic; "raise the specter of unemployment"; "he conjured
         wild birds in the air"; "call down the spirits from the
         mountain" [syn: raise, conjure, conjure up, invoke,
         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: invoke, 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, invoke]

Moby Thesaurus II by Grady Ward, 1.0:

97 Moby Thesaurus words for "invoke":
   accost, address, adjure, apostrophize, appeal, appeal to, approach,
   beg, beseech, bespeak, bid come, buttonhole, call, call away,
   call back, call for, call for help, call forth, call in, call on,
   call out, call to, call together, call up, call up spirits,
   call upon, cite, clamor for, commune with God, conjure, conjure up,
   conjure up spirits, convene, convoke, crave, cross-refer,
   cross-reference, cry for, cry on, cry to, demand,
   direct attention to, effect, entreat, evoke, give thanks, greet,
   hail, halloo, impetrate, implement, implore, importune, imprecate,
   indent, kneel to, make a cross-reference, make reference to,
   make supplication, muster, muster up, obtest, offer a prayer,
   order up, page, petition, plead, plead for, pray, pray over,
   preconize, raise, raise ghosts, recall, recite the rosary,
   refer to, reference, requisition, return thanks, run to, salute,
   say grace, send after, send for, serve, speak, speak fair,
   speak to, subpoena, summon, summon forth, summon spirits,
   summon up, summons, supplicate, take aside, talk to