mare vs nag

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. 

nag

noun
  • A small horse; a pony. 

  • Someone or something that nags. 

  • A persistent, bothersome thought or worry. 

  • An old, useless horse. 

  • A repeated complaint or reminder. 

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 mare and nag occurred in a corpus of books? (source: Google Ngram Viewer )