approval vs popularity

approval

noun
  • An expression of favorable acceptance and encouragement; a compliment that also condones. 

  • Something mailed by a seller to a collector to match their stated interests; the collector can approve of or return the item. 

  • An expression granting permission; an indication of agreement with a proposal; an acknowledgement that a person, thing, or event meets requirements. 

popularity

noun
  • The quality or state of being popular; especially, the state of being esteemed by, or of being in favor with, the people at large 

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