aevum vs eon

aevum

noun
  • The temporal mode of existence between time and eternity, said to be experienced by angels, saints, and celestial bodies (which medieval astronomy believed to be unchanging. 

eon

noun
  • Eternity. 

  • A period of 1,000,000,000 years. 

  • The longest geochronologic unit, being a period of hundreds of millions of years; subdivided into eras. 

  • A spirit being emanating from the Godhead. 

  • A long period of time. 

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