adage vs watchword

adage

noun
  • An old saying which has been overused or considered a cliché; a trite maxim. 

  • An old saying which has obtained credit by long use. 

watchword

noun
  • A word used as a motto, as expressive of a principle, belief, or rule of action; a rallying cry. 

  • A prearranged reply to the challenge of a sentry or a guard; a password or signal by which friends can be known from enemies. 

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