air conditioner vs propeller

air conditioner

noun
  • A machine that is used to control temperature and humidity in an enclosed space. 

propeller

noun
  • A mechanical device with evenly-shaped blades that turn on a shaft to push against air or water, especially one used to propel an aircraft or boat. 

  • One who, or that which, propels. 

  • A steamboat thus propelled; a screw steamer. 

  • A spinnerbait. 

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