den vs ladies' room

den

noun
  • A comfortable room not used for formal entertaining. 

  • Synonym of fort (“structure improvised from furniture, etc. for playing games.”) 

  • A group of Cub Scouts of the same age who work on projects together. 

  • A small cavern or hollow place in the side of a hill, or among rocks; especially, a cave used by a wild animal for shelter or concealment. 

  • A squalid or wretched place; a haunt. 

verb
  • To ensconce or hide oneself in (or as in) a den. 

ladies' room

noun
  • 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. 

  • A public lavatory intended for use by women. 

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