grassroots vs proletarian

grassroots

adj
  • Of, or relating to people or society at the local level, particularly in politics, social movements, etc.; of the grass roots. 

proletarian

adj
  • Of or relating to the proletariat. 

noun
  • A member of the proletariat. 

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