hexad vs quintet

hexad

noun
  • A group of six. 

  • An element or radical with the combining power of six units, i.e. six atoms of hydrogen. 

quintet

noun
  • Any group of five members 

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

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

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