ternion vs triad

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. 

triad

noun
  • A grouping of three. 

  • on a CRT display, a group of three neighbouring phosphor dots, coloured green, red, and blue. 

  • A chord consisting of a root tone, the tone two degrees higher, and the tone four degrees higher in a given scale. 

  • A branch of a Chinese underground criminal society, mostly based in Hong Kong. 

  • A word of three syllables. 

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