upbeat vs weakening

upbeat

noun
  • An unaccented beat at the start of a musical phrase. 

adj
  • Having a fast pace, tempo, or beat. 

  • Having a positive, lively, or perky tone, attitude, etc. 

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 upbeat and weakening occurred in a corpus of books? (source: Google Ngram Viewer )