platitude vs polyword

platitude

noun
  • An often-quoted saying that is supposed to be meaningful but has become unoriginal or hackneyed through overuse; a cliché. 

  • A claim that is trivially true, to the point of being uninteresting. 

  • Unoriginality; triteness. 

  • Flatness; lack of change, activity, or deviation. 

polyword

noun
  • A phrase that acts like a single word. 

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