prosaism vs shibboleth

prosaism

noun
  • A manner, quality, expression, style, phrase or word that is prosaic. 

shibboleth

noun
  • A common or longstanding belief, custom, or catchphrase associated with a particular group, especially one with little current meaning or truth. 

  • A particular pronunciation or custom that is regarded as distinguishing members of a group from non-members, especially when used as a test. 

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