grizzled vs senescent

grizzled

adj
  • greyed, old 

  • streaked or mixed with grey; grizzly; griseous 

  • grey or partly grey 

senescent

adj
  • Characteristic of old age. 

  • That ceases to divide. 

  • Growing old; decaying with the lapse of time. 

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