octet vs septenary

octet

noun
  • A group or set of eight of something. 

  • A composition for such a group of musicians. 

  • A group of eight musicians performing together. 

  • A byte of eight bits. Abbreviation: o 

  • A group of three bits, representing any of eight possible values. 

septenary

noun
  • A group of seven things. 

  • A period of seven years. 

  • The seven notes of the diatonic scale. 

adj
  • Of seventh rank or order. 

  • Consisting of or containing seven. 

  • Lasting seven years; continuing seven years. 

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