birth vs knock off

birth

verb
  • To bear or give birth to (a child). 

  • To produce, give rise to. 

adj
  • A familial relationship established by childbirth. 

noun
  • A beginning or start; a point of origin. 

  • The process of childbearing; the beginning of life. 

  • That which is born. 

  • An instance of childbirth. 

  • The circumstances of one's background, ancestry, or upbringing. 

knock off

verb
  • To have sex with. 

  • To rob. 

  • To defeat. 

  • To halt one's work or other activity. 

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