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]