serial killer vs slasher

serial killer

noun
  • A person who commits multiple (more than two) murders, especially similar ones with no obvious motive over a period of time with a "cooling-off" period between each murder. 

slasher

noun
  • A murderer in such a film. 

  • A tool for cutting undergrowth. 

  • One who slashes. 

  • A horror movie with graphic blood and violence; a slasher movie. 

  • A machine for applying size to warp yarns. 

  • One who self-injures by cutting. 

  • One who writes slash fiction and/or supports male/male ships. 

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