affiliation vs sorority

affiliation

noun
  • The relationship resulting from affiliating one thing with another. 

  • A club, society or umbrella organisation so formed, especially a trade union. 

  • The establishment of a child's paternity or maternity 

sorority

noun
  • A group of girls or women associated for a common purpose; a sisterhood. 

  • A social organization of female students at a college or university; usually identified by Greek letters. 

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