Dictionary.net

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.

1. A stimulant. 2. Anything which arouses action (the response) in a muscle, nerve, or gland, or which promotes some trophic change.

That which stimulates an organ.

A goad: anything that rouses the mind, or that excites to action: a stimulant:-pl. STIMULI.

Anything that rouses to action.

Anything that rouses or excites.

Something which stimulates; a stimulant; a sting.

In med., that which produces a sudden but transitory increase of vital action; anything that excites to action; a stimulant; in bot., applied to stinging hairs with an irritating secretion at the base.

An agent which causes a body or some part of it to react when affected by it.

Any thing which excites the animal economy.

Any agent producing reaction in an irritable tissue.

An agent or agency that stimulates.

The action or result of a stimulant; stimulation.

n. [Latin, Greek] A goad; hence, something that rouses the mind or spirits ;-that which produces an increase of vital action ;-in botany, a sting ; a prickle.