impact vs knock out

impact

verb
  • To collide or strike, the act of impinging. 

  • To stamp or impress onto something. 

  • To significantly or strongly influence or affect; to have an impact on. 

  • To compress; to compact; to press into something or pack together. 

noun
  • A significant or strong influence or effect. 

  • A forced impinging. 

  • The striking of one body against another; collision. 

  • The force or energy of a collision of two objects. 

knock out

verb
  • To strike or bump (someone or something) out. 

  • To fall asleep, especially suddenly. 

  • To lose the scent of hounds in fox-hunting. 

  • To eliminate from a contest or similar. 

  • To put to sleep. 

  • To complete, especially in haste; knock off. 

  • To render unconscious, as by a blow to the head. 

  • To exhaust. 

  • To cause a mechanism to become non-functional by damaging or destroying it. 

  • To communicate (a message) by knocking. 

How often have the words impact and knock out occurred in a corpus of books? (source: Google Ngram Viewer )