abstain vs knock off

abstain

verb
  • Refrain from (something or doing something); keep from doing, especially an indulgence. 

  • Deliberately refrain from casting one's vote at a meeting where one is present. 

knock off

verb
  • To halt one's work or other activity. 

  • To rob. 

  • To defeat. 

  • 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 abstain and knock off occurred in a corpus of books? (source: Google Ngram Viewer )