aevum vs perpetuity

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. 

perpetuity

noun
  • The quality or state of being perpetual; endless duration; uninterrupted existence. 

  • An annuity in which the periodic payments begin on a fixed date and continue indefinitely. 

  • Something that is perpetual. 

  • A limitation intended to be unalterable and of indefinite duration; a disposition of property which attempts to make it inalienable beyond certain limits fixed or conceived as being fixed by the general law. 

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