hobby vs hobby horse

hobby

noun
  • An extinct breed of horse native to the British Isles, also known as the Irish Hobby 

  • An activity that one enjoys doing in one's spare time. 

  • Any of four species of small falcons in the genus Falco, especially Falco subbuteo. 

hobby horse

noun
  • The Irish hobby, an extinct breed of horse. 

  • A topic about which someone loves to talk at great length. 

  • A child's toy consisting of a (usually wooden or cloth) horse's head mounted on a stick. 

  • A puppet-like costume used in some traditional dances and festivals that gives its wearer the appearance of a man on horseback. 

  • An early bicycle with no pedals or brakes; a draisienne. 

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