VI vs hexad

VI

name

  • VI (“U.S. Virgin Islands”) 

noun

  • verb, intransitive. 

hexad

noun

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

  • A group of six. 

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