1. (n.) An incentive; that which provokes or excites -- not usually meaning a drug\; as, the hope of gain is a powerful stimulus to labor and action.

2. (v. t.) 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.

activator aggravation agitation animation animator antecedents arousal arouser arousing bait base basis boost bribe call carrot catalyst causation cause cause and effect determinant determinative electrification element encouragement energizer etiology exacerbation exasperation excitation excitement exhilaration factor fillip fomentation galvanization goad ground grounds human dynamo impetus impulse incentive incitation incitement inducement inflammation infuriation instigation interest invitation irritation lathering up life lure motivating force motivation motive motive power occasion payment percentage persuasive perturbation principle profit propellant provocation provocative push restorative reward spark plug spur steaming up stimulant stimulation stimulative stimulator stirring stirring up sweetener sweetening tonic urging whet whipping up working up