serial killer vs terminator

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. 

terminator

noun
  • Someone who terminates or ends something, especially (in later use) an assassin or exterminator. 

  • An electrical device that absorbs reflection at the end of a transmission line. 

  • The line between the day side and the night side of a moon, planet or other celestial body. 

  • A text character that serves to mark the end of a document or transmission. 

  • A DNA sequence which causes RNA transcription to cease and an mRNA transcript to break off. 

  • An intelligent android created to destroy humans. 

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