descending vs lessening

descending

noun
  • A descent. 

adj
  • Ordered such that each element is less than or equal to the previous element. 

  • Moving or sloping downwards. 

  • Becoming lower in pitch. 

  • Causing a sequence to follow a descending order. 

lessening

noun
  • A growing lesser; reduction or decrease. 

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