noun An external phenomenon that has an influence on a system, by triggering or modifying an internal phenomenon; for example, a spur or incentive that drives a person to take action or change behaviour.
an economic stimulus
noun Something external that elicits or influences a physiological or psychological activity or response, or that affects any of the sensory apparatuses.
to respond to a stimulus
noun A stinging part on the body of a plant or insect.