sestet vs villanelle

sestet

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

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

villanelle

noun
  • A type of poem, consisting of five tercets and one quatrain, with only two rhymes. 

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