incentive vs perquisite

incentive

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

  • Something that motivates, rouses, or encourages. 

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

  • Serving to kindle or set on fire. 

perquisite

noun
  • Any monetary or other incidental benefit beyond salary. 

  • A privilege or possession held or claimed exclusively by a certain person, group or class. 

  • A gratuity. 

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