ternion vs troika

ternion

noun
  • The number three; three things together; a ternary or triplet. 

  • A section of paper for a book containing three double leaves or twelve pages. 

troika

noun
  • A party or group of three, especially a ruling council of three people in Russian contexts. 

  • A Russian carriage drawn by a team of three horses abreast. 

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