counterfeit vs knock off

counterfeit

verb
  • To falsely produce what appears to be official or valid; to produce a forged copy of. 

  • Of a turn or river card, to invalidate a player's hand by making a better hand on the board. 

adj
  • Inauthentic. 

  • False, especially of money; intended to deceive or carry appearance of being genuine. 

  • Assuming the appearance of something; deceitful; hypocritical. 

noun
  • A non-genuine article; a fake. 

  • One who counterfeits; a counterfeiter. 

knock off

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

  • To rob. 

  • To defeat. 

  • To halt one's work or other activity. 

  • To have sex with. 

  • To remove, as a discount or estimate. 

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

  • To remove by hitting (something, someone) 

  • To kill. 

  • To accomplish hastily. 

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