mare vs yearling

mare

noun
  • An adult female horse. 

  • On Saturn's moon Titan, any of several lakes which are large expanses of what is thought to be liquid hydrocarbons. 

  • A nightmare; a frustrating or terrible experience. 

  • A foolish woman. 

  • A large, dark plain, which may have the appearance of a sea. 

yearling

noun
  • A racehorse that is considered to be one year old until a subsequent January 1st. 

  • A sophomore at West Point military academy. 

  • An animal that is between one and two years old; one that is in its second year (but not yet two full years old). 

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