backside vs prat

backside

noun
  • A person's buttocks. 

  • Used other than figuratively or idiomatically: see back, side. 

  • The back side of an estate: the backyard and outbuildings behind a main house, especially (UK dialect, euphemistic) an outhouse. 

  • The reverse or opposite of anything. 

adj
  • Used other than figuratively or idiomatically: see back, side. 

  • Approaching an obstacle backward 

prat

noun
  • A buttock, or the buttocks; a person's bottom. 

  • A cunning or mischievous trick; a prank, a joke. 

  • The female genitals. 

  • A fool. 

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