airship vs autogiro

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. 

autogiro

noun
  • An aircraft in which lift is provided by unpowered rotating wings and thrust is provided by a conventional propeller. 

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