North American football vs gridiron

North American football

noun
  • Collectively, Canadian football and American football. 

gridiron

noun
  • An openwork frame on which vessels are placed for examination, cleaning, and repairs. 

  • American and Canadian football, particularly when used to distinguish from other codes of football. 

  • A raised framework from which lighting is suspended. 

  • The field on which American football is played. 

  • An iron rack or grate used for broiling meat and fish over coals. 

  • An instrument of torture on which people were secured before being burned by fire. 

  • Any object resembling the rack or grate. 

verb
  • To mark or cover with lines; to crisscross. 

  • To purchase land so that the remaining adjacent sections are smaller than the minimum area purchasable as freehold, thus excluding potential freeholders. 

How often have the words North American football and gridiron occurred in a corpus of books? (source: Google Ngram Viewer )