motto vs prosaism

motto

noun
  • A sentence, phrase, or word, prefixed to an essay, discourse, chapter, canto, or the like, suggestive of its subject matter; a short, suggestive expression of a guiding principle; a maxim. 

  • A sentence, phrase, or word, forming part of an heraldic achievement. 

prosaism

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

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