murder vs serial killer

murder

noun
  • The crime of deliberately killing a person without moral justification. 

  • The act of deliberate killing of a person or other being without moral justification, especially with malice aforethought. 

  • Something terrible to endure. 

  • A group of crows; the collective noun for crows. 

  • The commission of an act which abets the commission of a crime the commission of which causes the death of a human. 

verb
  • To botch or mangle. 

  • To devour, ravish. 

  • To kick someone's ass or chew someone out (used to express one’s anger at somebody). 

  • To defeat decisively. 

  • To deliberately kill (a person or persons) without justification, especially with malice aforethought. 

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. 

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