Definition of: stimulus

(stim′yə·ləs) noun plural ·li (-lī)
1. Anything that rouses the mind or spirits; an incentive; a stimulant; a sting; a spur, or goad.
2. Physiol. a Any agent or form of excitation which influences the activity of an organism as a whole or in any of its parts. b That which initiates an impulse, as in a nerve or muscle, or produces an altered state of consciousness, as by arousing new or stronger sensations. [<L]