incentive vs warning

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. 

warning

noun
  • Something spoken or written that is intended to warn. 

  • The action of the verb warn; an instance of warning someone. 

intj
  • Used to warn of danger in signs and notices. 

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