ethnic group vs sept

ethnic group

noun
  • A group of people who identify with one another, especially on the basis of ancestral, national, cultural, historical or religious grounds. 

sept

noun
  • A clan, tribe, or family, proceeding from a common progenitor; especially, one of the ancient clans of Ireland. 

  • An enclosure; a railing. 

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