filch vs knock off

filch

verb
  • To illegally take possession of (something, especially items of low value); to pilfer, to steal. 

noun
  • Something which has been filched or stolen. 

  • An act of filching; larceny, theft. 

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. 

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