contract killing vs grievance

contract killing

noun
  • The act of hiring or procuring a contract killer. 

grievance

noun
  • A formal complaint, especially in the context of a unionized workplace. 

  • Feelings of being wronged; outrage. 

  • A wrong or hardship suffered, which is the grounds of a complaint. 

  • Violation of regulations or objectionable behavior. 

  • A complaint or annoyance. 

  • Something which causes grief. 

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