heptad vs quintet

heptad

noun
  • A sequence of seven bases. 

  • Synonym of septet: a group of seven things. 

quintet

noun
  • A composition (a type of chamber music) in five parts (typically each a singer or instrumentalist, sometimes several musicians) 

  • A group of five musicians, fit to play such a piece of music together 

  • Any group of five members 

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