cavern vs root cellar

cavern

verb
  • To put into a cavern. 

  • To form a cavern or deep depression in. 

noun
  • A large, dark place or space. 

  • A large cave. 

  • An underground chamber. 

root cellar

verb
  • To cellar (food) in a root cellar. 

noun
  • A structure built underground or partially underground and used to store vegetables, fruits, and nuts or other foods. 

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