knock off vs liberate

knock off

verb
  • 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. 

  • To accomplish hastily. 

liberate

verb
  • To acquire from another by theft or force: to steal, to rob. 

  • To release from chemical bonds or solutions. 

  • To acquire from an enemy during wartime, used especially of cities, regions, and other population centers. 

  • To release from servitude or unjust rule. 

  • To release from slavery: to manumit. 

  • To release from restraint or inhibition. 

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