The Collaborative International Dictionary of English v.0.48:

Instigation \In`sti*ga"tion\, n. [L. instigatio: cf. F.
   instigation.]
   The act of instigating, or the state of being instigated;
   incitement; esp. to evil or wickedness.
   [1913 Webster]

         The baseness and villainy that . . . the instigation of
         the devil could bring the sons of men to. --South.
   [1913 Webster]

WordNet (r) 3.0 (2006):

instigation
    n 1: the verbal act of urging on [syn: abetment, abettal,
         instigation]
    2: deliberate and intentional triggering (of trouble or discord)
       [syn: fomentation, instigation]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "instigation":
   agitation, arousal, catalyst, exasperation, excitation, excitement,
   firing, fomentation, goad, impetus, impulse, incentive, incitation,
   incitement, inflammation, irritation, pep rally, pep talk,
   provocation, rabble-rousing, spur, stimulation, stirring,
   stirring-up



Bouvier's Law Dictionary, Revised 6th Ed (1856):

INSTIGATION. The act by which one incites another to do something, as to
injure a third person, or to commit some crime or misdemeanor, to commence
a suit or to prosecute a criminal. Vide Accomplice.