affair vs flirtation

affair

noun
  • Any proceeding or action which it is wished to refer to or characterize vaguely. 

  • An action or engagement not of sufficient magnitude to be called a battle. 

  • An adulterous relationship (from affaire de cœur, affair of the heart). 

  • A person with whom someone has an adulterous relationship. 

  • A romantic relationship with someone who is not one's regular partner (boyfriend, girlfriend). 

  • Something which is done or is to be done; business of any kind, commercial, professional, or public. 

  • A party or social gathering, especially of a formal nature. 

  • A material object (vaguely designated). 

flirtation

noun
  • A period of experimentation with or interest in a particular idea or activity. 

  • Playing at courtship; coquetry. 

  • An instance of flirting. 

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