declivity vs descending

declivity

noun
  • The downward slope of a hill; the downward slope of a curve. 

  • A downward bend in a path. 

  • An inward curve of the exoskeleton of an insect, such as between body segments; a segment of an insect's body where the exoskeleton curves inward. 

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. 

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