monadnock vs sierra

monadnock

noun
  • A hill or mountain standing isolated above a predominantly flat plain. 

sierra

noun
  • A rugged range of mountains. 

  • A relatively low-quality grade of Spanish saffron. 

  • A scombroid fish. 

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