downfall vs strengthening

downfall

verb
  • To fall down; deteriorate; decline. 

noun
  • The cause of such a fall; a critical blow or error. 

  • A precipitous decline in fortune; death or rapid deterioration, as in status or wealth. 

  • An act of falling down. 

strengthening

noun
  • The process by which something is strengthened. 

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