greenhouse vs ripen

greenhouse

verb
  • To nurture in order to promote growth. 

  • To place (plants) in a greenhouse. 

noun
  • A building used to grow plants, particularly one with large glass windows or plastic sheeting to trap heat from sunlight even in intemperate seasons or climates. 

  • A hot state in global climate. 

  • A structure that shields the operating table to protect against bacteria. 

ripen

verb
  • to grow ripe; to become mature (said of grain, fruit, flowers etc.) 

  • To cause (something) to mature; to make ripe 

  • To approach or come to perfection. 

  • To mature; to fit or prepare; to bring to perfection 

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