playground vs quadrangle

playground

noun
  • A large open space for children to play on, usually having dedicated play equipment (such as swings and slides). 

  • Any physical or metaphysical space in which a person or organization has free rein to do as they please. 

quadrangle

noun
  • The buildings forming the border of such a courtyard. 

  • A geometric shape with four angles and four straight sides; a four-sided polygon. 

  • A courtyard which is quadrangular. 

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