affair vs incident

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). 

incident

noun
  • A (relatively minor) event that is incidental to, or related to others. 

  • An event that causes or may cause an interruption or a crisis, such as a workplace illness or a software error. 

  • An event or occurrence. 

adj
  • Dependent upon, or appertaining to, another thing, called the principal. 

  • Liable to happen; apt to occur; befalling; hence, naturally happening or appertaining. 

  • Arising as the result of an event, inherent. 

  • Coming or happening accidentally; not in the usual course of things; not in connection with the main design; not according to expectation; casual; fortuitous. 

  • Falling on or striking a surface. 

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