close-stool vs necessarium

close-stool

noun
  • A chamber pot enclosed in a stool or box; a commode. 

necessarium

noun
  • A lavatory. 

  • Synonym of reredorter: a monastery's latrine, outhouse, or lavatory, typically located behind the dormitory. 

How often have the words close-stool and necessarium occurred in a corpus of books? (source: Google Ngram Viewer )