senescent vs superannuated

senescent

adj
  • Characteristic of old age. 

  • That ceases to divide. 

  • Growing old; decaying with the lapse of time. 

superannuated

adj
  • Retired or discarded due to age. 

  • Obsolete, antiquated. 

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