kickback vs protection money

kickback

noun
  • A covert, often illegal, payment in return for a favor consisting of providing an opportunity of chargeable transaction; a kind of bribe. 

  • A backward kick, a retrograde movement of an extremity. 

  • recoil; a sudden backward motion, usually in the direction of the operator. 

  • An accident wherein the upper tip of the bar of a running chainsaw contacts a relatively immovable object, forcing the bar upwards and pressing the running chain more firmly against the object, causing the saw to be hurled upwards and backwards into the operator's face. 

  • A dangerous buildup of gas pressure at the wellhead. 

  • In contract bridge, an ace asking convention initiated by the first step above four of the agreed trump suit. 

  • An accident where an object being cut by a rotating blade or disk, such as a circular saw, is caught by the blade and thrown outward. 

  • The board separating one bowling lane from another at the pit end. 

  • A feature that saves the ball from draining and propels it back into play. 

  • A relaxed party. 

protection money

noun
  • Money paid, especially at regular intervals, to criminals or to corrupt officials who threaten to cause harm to the payer or to his or her business if the money is not paid. 

How often have the words kickback and protection money occurred in a corpus of books? (source: Google Ngram Viewer )