comeback vs weakening

comeback

noun
  • A return (e.g. to popularity, success, etc.) after an extended period of obscurity. 

  • A retort or answer, particularly a quick or clever one. 

  • An occurrence of an athlete or sports team in a competition overcoming a substantial disadvantage in points to win or draw. 

weakening

noun
  • A structural principle of mathematical logic that states that the hypotheses of any derived fact may be freely extended with additional assumptions. 

  • An instance or process of loss of strength. 

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