extort vs hold to ransom

extort

verb
  • To obtain by means of the offense of extortion. 

  • To take or seize from an unwilling person by physical force, menace, duress, torture, or any undue or illegal exercise of power or ingenuity. 

  • To twist outwards. 

hold to ransom

verb
  • To hold (someone) hostage until a ransom is paid. 

How often have the words extort and hold to ransom occurred in a corpus of books? (source: Google Ngram Viewer )