busk vs knock off

busk

verb
  • To tack, cruise about. 

  • To solicit money by entertaining the public in the street or in public transport. 

noun
  • A strip of metal, whalebone, wood, or other material, worn in the front of a corset to stiffen it. 

  • A corset. 

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