noun, plural: stimulants
(1) A substance capable of creating a stimulus that increases physiological or nervous activity in the body.
(2) An agent that produces stimulation.
Example is caffeine in tea and coffee capable of stimulating the central nervous system, increasing heart rate, blood pressure, and alertness, and therefore, making some people feel better and able to concentrate.
Drugs that act as stimulants can temporarily increase alertness and awareness, or temporarily increase body or organ function.
Word origin: Latin stimulant- (s. of stimulāns, prp. of stimulāre to goad).