cold cash vs greenback

cold cash

noun
  • Money, especially in the form of paper currency or coins, which is in hand or readily available for use. 

greenback

noun
  • A unit of American currency issued during the Civil War by the Treasury Department. 

  • The United States dollar. 

  • A wave that has not yet begun to break. 

  • Any bill that is legal tender in the US (originally printed with green and black ink) issued by the Federal Reserve. 

How often have the words cold cash and greenback occurred in a corpus of books? (source: Google Ngram Viewer )