polling vs referendum

polling

noun
  • the process of voting in an election. 

  • The action of taking a poll. 

  • A technique that continually interrogates a peripheral or service to see if it has data to transfer. 

referendum

noun
  • A direct popular vote on a proposed law or constitutional amendment. The adposition on is usually used before the related subject of the vote. 

  • An action, choice, etc., which is perceived as passing judgment on another matter. 

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