low water vs weakening

low water

noun
  • The temporary situation of having little money. 

  • The lowest stage of a river. 

  • The location of low tide in a coastal area. 

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