hobby horse vs nag

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. 

nag

noun
  • An old, useless horse. 

  • Someone or something that nags. 

  • A persistent, bothersome thought or worry. 

  • A repeated complaint or reminder. 

  • A small horse; a pony. 

verb
  • To bother with persistent thoughts or memories. 

  • Anyone would think that I nagged at you, Amanda! (From Amanda! by Robin Klein) 

  • a nagging pain in his left knee 

  • To repeatedly remind or complain to (someone) in an annoying way, often about insignificant or unnecessary matters. 

  • The notion that he forgot something nagged him the rest of the day. 

  • To bother or disturb persistently in any way. 

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