assist vs knock off

assist

verb
  • To help. 

  • To make a pass that leads directly towards scoring. 

  • To help compensate for what is missing with the help of a medical technique or therapy. 

noun
  • A decisive pass made to the goal scorer 

  • A helpful action or an act of giving. 

  • A defensive play, allowing a teammate to record a putout. 

knock off

verb
  • To accomplish hastily. 

  • To rob. 

  • To defeat. 

  • To halt one's work or other activity. 

  • To have sex with. 

  • To remove, as a discount or estimate. 

  • To make a copy of, as of a design. 

  • To assign (an item) to a bidder at an auction, indicated by knocking on the counter. 

  • To remove by hitting (something, someone) 

  • To kill. 

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