elementary vs grass-roots

elementary

noun
  • A supernatural being which is associated with the elements. 

  • An elementary school 

adj
  • Relating to the basic, essential or fundamental part of something. 

  • Relating to an elementary school. 

  • Relating to a subatomic particle. 

grass-roots

How often have the words elementary and grass-roots occurred in a corpus of books? (source: Google Ngram Viewer )