lavvy vs necessarium

lavvy

noun
  • A lavatory: a room used for urination and defecation. 

  • A toilet: a fixture used for urination and defecation. 

necessarium

noun
  • A lavatory. 

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

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