aevum vs sempiternity

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. 

sempiternity

noun
  • Existence within time but infinitely into the future, as opposed to eternity, understood as existence outside time. 

  • Eternity; a seemingly everlasting period of time. 

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