footy vs rugby union

footy

noun
  • The game or sport of football, usually Australian rules football or rugby league, but not soccer 

  • A football fan. 

  • Football (association football) (soccer in US, Canada, Australia, New Zealand) 

  • The ball used in a game of footy. 

  • A short sock. 

rugby union

noun
  • A form of rugby football, historically amateur, having 15 players per side; points are scored for a try, penalty, drop kick or conversion. 

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