cadre vs key group

cadre

noun
  • The framework or skeleton upon which a new regiment is to be formed; the officers of a regiment forming the staff. 

  • The core of a managing group, or a member of such a group. 

  • A small group of people specially trained for a particular purpose or profession. 

  • A frame or framework. 

key group

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