cucumber vs greenback

cucumber

noun
  • A vine in the gourd family, Cucumis sativus. 

  • The edible fruit of this plant, having a green rind and crisp white flesh. 

  • A person who is calm and self-possessed. 

greenback

noun
  • The United States dollar. 

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

  • 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 cucumber and greenback occurred in a corpus of books? (source: Google Ngram Viewer )