grail vs the object of the exercise

grail

noun
  • Small particles of earth; gravel. 

  • One of the small feathers of a hawk. 

  • Something eagerly sought or quested for. 

  • The Holy Grail. 

  • A book of offices in the Roman Catholic Church; a gradual. 

the object of the exercise

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