D defs.my
Entry 2 senses Webster, 1913

Stimulus

/stĭm'-yəl-əs/ · Stim·u·lus · IPA /ˈstɪm.jə.ləs/
01 n. A goad; hence, something that rouses the mind or spirits; an incentive; as, the hope of gain is a powerful stimulus to labor and action.
pl. Stimuli ((#))
  1. 1.
    A goad; hence, something that rouses the mind or spirits; an incentive; as, the hope of gain is a powerful stimulus to labor and action.
  2. 2.
    That which excites or produces a temporary increase of vital action, either in the whole organism or in any of its parts; especially (Physiol.), any substance or agent capable of evoking the activity of a nerve or irritable muscle, or capable of producing an impression upon a sensory organ or more particularly upon its specific end organ.(Physiol.)