The Collaborative International Dictionary of English v.0.48:

Stimulation \Stim`u*la"tion\, n. [L. stimulatio: cf. F.
   stimulation.]
   1. The act of stimulating, or the state of being stimulated.
      [1913 Webster]

   2. (Physiol.) The irritating action of various agents
      (stimuli) on muscles, nerves, or a sensory end organ, by
      which activity is evoked; especially, the nervous impulse
      produced by various agents on nerves, or a sensory end
      organ, by which the part connected with the nerve is
      thrown into a state of activity; irritation.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stimulation
    n 1: the act of arousing an organism to action
    2: any stimulating information or event; acts to arouse action
       [syn: stimulation, stimulus, stimulant, input]
    3: (physiology) the effect of a stimulus (on nerves or organs
       etc.)
    4: mutual sexual fondling prior to sexual intercourse [syn:
       foreplay, arousal, stimulation]

Moby Thesaurus II by Grady Ward, 1.0:

119 Moby Thesaurus words for "stimulation":
   a high, actuation, aggravation, agitation, alpha decay, animation,
   arousal, arousing, atom-chipping, atom-smashing,
   atomic disintegration, atomic reaction, atomization, bait,
   beta decay, bombardment, bracer, bracing, breeding, bribe, bullet,
   carrot, chain reaction, cleavage, cordial, direction,
   disintegration series, dissociation, electrification, emotion,
   encouragement, energizing, enlivenment, exacerbation, exasperation,
   exchange reaction, excitation, excitedness, excitement,
   exhilaration, fillip, firing, fission, fission reaction,
   fomentation, galvanization, gamma decay, incentive, incitation,
   incitement, inducement, inflammation, influence, infuriation,
   inner-direction, instigation, interest, invigoration, invitation,
   ionization, irritation, lathering up, lure, manic state,
   motivation, moving, neutron reaction, nonreversible reaction,
   nuclear fission, nucleization, other-direction, payment, pep rally,
   pep talk, percentage, persuasive, perturbation,
   photodisintegration, pick-me-up, profit, prompting, proton gun,
   proton reaction, provocation, quickening, rabble-rousing,
   reanimation, recreation, refection, refreshing, refreshment,
   regale, regalement, reinvigoration, renewal, reversible reaction,
   revitalization, revival, revivescence, revivescency,
   revivification, reward, splitting the atom, steaming up,
   stimulative, stimulus, stirring, stirring up, stirring-up,
   sweetener, sweetening, target, thermonuclear reaction, tonic,
   vitalization, vivification, whet, whipping up, working up