ladies' room vs necessarium

ladies' room

noun
  • A public lavatory intended for use by women. 

  • A room belonging to or intended for some or all women 

  • A waiting room in a railway station or other public building intended exclusively for women and usually including a separate women's lavatory. 

necessarium

noun
  • A lavatory. 

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

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