septet vs sestet

septet

noun
  • A composition for a group of seven musicians. 

  • A group of seven musicians. 

  • A set of seven lines. 

sestet

noun
  • A piece of music composed for six voices or six instruments; a sextet or sestuor. 

  • The last six lines of a sonnet, forming two stanzas of three lines each. 

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