stimulus

Etymology

Borrowed from Latin stimulus (“goad, prick”).

noun

1. 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
   Democrats, meanwhile, point out that Republicans seem to have made a conscious decision, beginning with the stimulus, to oppose anything the president put forward, dooming any chance of renewed cooperation between the parties. November 7, 2012, Matt Bai, “Winning a Second Term, Obama Will Confront Familiar Headwinds”, in New York Times
2. (physiology, psychology, medicine) Something external that elicits or influences a physiological or psychological activity or response, or that affects any of the sensory apparatuses.
   Even light nonpainful stimuli can provoke or exacerbate spontaneous pain; this is not limited to tactile, thermal, or vibratory stimuli, because auditory, visual, olfactory, and visceral stimuli also may be problematic. 2002, Kim Burchiel, Surgical Management of Pain, Thieme, page 44
3. (botany, entomology) A sting on the body of a plant or insect.
   Many plants, like many animals, are furnished with arms for their protection; these are either aculei, prickles […]; or stimuli, stings, as in the nettles, which are armed with a venomous fluid for the annoyance of naked animals. 1789, Erasmus Darwin, The Loves of the Plants, J. Johnson, page 15