airship vs ramjet

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. 

ramjet

noun
  • A jet engine in which forward motion forces air into an inlet, compressing it (as opposed to having a pump type device compressing the air for combustion with fuel), and where combustion is subsonic. 

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