ark vs bolthole

ark

noun
  • Something affording protection; safety, shelter, refuge 

  • A decorated cabinet at the front of a synagogue, in which Torah scrolls are kept. 

  • The Ark of the Covenant. 

  • A spacious type of boat with a flat bottom. 

  • A large box with a flat lid. 

  • Noah's Ark: the ship built by Noah to save his family and a collection of animals from the deluge. 

bolthole

noun
  • A second home, etc. where a person can go to escape the stresses of everyday life. 

  • A hole in an animal's den, or through a wall or fence, used for escape or emergency exit; i.e. a hole the animal may bolt through. 

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