refrain vs watchword

refrain

noun
  • A much repeated comment, complaint, or saying. 

  • The chorus or burden of a song repeated at the end of each verse or stanza. 

verb
  • To stop oneself from some action or interference; to abstain. 

  • To abstain from (food or drink). 

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 refrain and watchword occurred in a corpus of books? (source: Google Ngram Viewer )