centenarian vs centennium

centenarian

noun
  • One who or that which is at least 100 years old. 

adj
  • Aged 100 years or more; extremely old. 

  • Of or relating to centenarians or a centenary celebration. 

centennium

noun
  • Synonym of century: A period of 100 years. 

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