something that incites to action or exertion or quickens action, feeling, thought, etc.

The approval of others is a potent stimulus.

Physiology, Medicine/Medical . something that excites an organism or part to functional activity.

noun

discouragement , hindrance , tranquilizer

noun

bang * , boost , catalyst , cause , charge , encouragement , eye-opener , fillip , fireworks * , flash * , goad , impetus , impulse , incentive , incitation , incitement , inducement , instigation , invitation , kick * , motivation , motive , piquing , propellant , push , shot in the arm , spur , stimulant , stimulation , sting * , turn-on , urgingnotes:a stimulant is a drug; a stimulus is anything encouraging an action (but rarely is it a drug) , prod , stimulator , provocation , trigger , cue , pl. stimuli , sting