den vs vacancy

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. 

vacancy

noun
  • An available room in a hotel; guest house, etc. 

  • Empty space. 

  • An unoccupied position or job. 

  • Lack of intelligence or understanding. 

  • A blank mind, unoccupied with thought. 

  • A defect in a crystal caused by the absence of an atom in a lattice 

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