(1):

(n.) The act of stimulating, or the state of being stimulated.

(2):

(n.) 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.