cutthroat vs killer instinct

cutthroat

noun
  • A murderer who slits the throats of victims. 

  • An unscrupulous, ruthless or unethical person. 

  • A three-player pocket billiards game where the object is to be the last player with at least one ball still on the table. 

adj
  • Involving the cutting of throats. 

  • Ruthlessly competitive, dog-eat-dog. 

  • Of or relating to a card game where everyone plays for him or herself rather than playing with a partner. 

killer instinct

noun
  • Used other than figuratively or idiomatically: see killer, instinct. 

  • The natural inclination to do whatever is necessary to succeed (including extreme violence) 

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