centennium vs superannuation

centennium

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

superannuation

noun
  • The condition or of being superannuated; old age or obsolescence. 

  • A retirement benefit fund, an accumulation of regular deductions from one′s wage or salary while employed and similar regular contributions from the employer, usually administered by an independent entity; a pension. 

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