incentive vs stimulus

incentive

noun
  • Something that motivates, rouses, or encourages. 

  • A bonus or reward, often monetary, to work harder. 

adj
  • Inciting; encouraging or moving; rousing to action; stimulating. 

  • Serving to kindle or set on fire. 

stimulus

noun
  • Something external that elicits or influences a physiological or psychological activity or response, or that affects any of the sensory apparatuses. 

  • A sting on the body of a plant or insect. 

  • 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. 

How often have the words incentive and stimulus occurred in a corpus of books? (source: Google Ngram Viewer )