highway robbery vs unreasonable

highway robbery

noun
  • The act of robbing a traveler on a public road. 

  • Said of excessive or exorbitant prices. 

unreasonable

adj
  • Without the ability to reason; unreasoning. 

  • Not reasonable; going beyond what could be expected or asked for. 

How often have the words highway robbery and unreasonable occurred in a corpus of books? (source: Google Ngram Viewer )