incentive vs strenuous

incentive

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

  • Serving to kindle or set on fire. 

noun
  • Something that motivates, rouses, or encourages. 

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

strenuous

adj
  • Having great vigour or energy; forceful. 

  • Requiring great exertion; very laborious 

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