monastery vs sacellum

monastery

noun
  • A building for housing monks or others who have taken religious vows. 

sacellum

noun
  • A small chapel, as a monument within a church. 

  • In Ancient Rome, a shrine open to the sky, sometimes used for sacrificial purposes, or in honor of the divine. 

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