airship vs supersonic

airship

noun
  • A lighter-than-air aircraft that can be propelled forward through the air as well as steered. 

  • A police air unit, a police helicopter 

  • Any aircraft. 

  • A high ranking official of the RAF, viewed as arrogant and distant. 

verb
  • To transport goods by aircraft. 

supersonic

noun
  • An aircraft that can travel at the speed of sound. 

adj
  • Ultrasonic, having a frequency too high to be audible. 

  • Greater than the speed of sound (in the same medium, and at the same temperature and pressure). 

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