poster child vs quiddity

poster child

noun
  • One who is a prototypical or quintessential example of something. 

quiddity

noun
  • The essence or inherent nature of a person or thing. 

  • A trifle; a nicety or quibble. 

  • An eccentricity; an odd feature. 

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