degeneration vs retrogradation

degeneration

noun
  • Gradual deterioration, from natural causes, of any class of animals or plants or any particular organ or organs; hereditary degradation of type. 

  • The process or state of growing worse, or the state of having become worse. 

  • That condition of a tissue or an organ in which its vitality has become either diminished or perverted; a substitution of a lower for a higher form of structure. 

  • A thing that has degenerated. 

retrogradation

noun
  • Decline, degradation. 

  • A reaction that takes place in gelatinized starch when the amylose and amylopectin chains realign themselves, largely responsible for bread becoming stale. 

  • Motion in a retrograde manner. 

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