aeriform vs pneumatic

aeriform

adj
  • Having a form similar to that of air. 

  • Pertaining to air. 

  • Light, unsubstantial, or unstable. 

pneumatic

adj
  • Of, relating to, or resembling air or other gases 

  • Powered by, or filled with, compressed air 

  • well-rounded; full-breasted; bouncy 

  • Of or relating to pneumatics 

  • Spiritual; of or relating to the pneuma 

  • Having cavities filled with air 

noun
  • In the gnostic theologian Valentinus' triadic grouping of man, the highest type; a person focused on spiritual reality (the other two being hylic and psychic). 

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