decennary vs decenniad

decennary

noun

  • A decennium: a period of ten years. 

adj

  • Decennial: of or related to a ten-year period. 

decenniad

noun

  • Synonym of decade: a period of 10 years. 

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