(Latin: impel, goad, sting, spur, incentive, full of incentives)

stimulus (s), stimuli (pl)
1. Any form of energy capable of eliciting a reaction in a sense organ or in any excitable tissue.
2. A signal that alerts an organism or leads to a responsive action: "Heat and light are physical stimuli for a variety of responses."
3. Something that encourages an activity or a process to begin, to increase, or to develop: "The dog responded to the stimulus of the whistle."
4. An agent or factor that provokes interest, enthusiasm, or excitement.
5. Anything that causes something to happen, to progress, or to become more active: "When our company had a pay raise, it was a stimulus for greater production."
1. Exciting vasomotor action.
2. An agent that excites the vasomotor nerves to action.

Vasomotor, refers to something affecting the calibre (diameter) of a vessel, especially of a blood vessel.