phratry vs sept

phratry

noun
  • A clan or kinship group consisting of a number of families claiming descent from a common ancestor and having certain collective functions and responsibilities. 

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 phratry and sept occurred in a corpus of books? (source: Google Ngram Viewer )