Definitions of event:

• noun:   something that happens at a given place and time
• noun:   a phenomenon located at a single point in space-time; the fundamental observational entity in relativity theory
• noun:   a special set of circumstances

  Example: "In that event, the first possibility is excluded"

• noun:   a phenomenon that follows and is caused by some previous phenomenon

  Example: "He acted very wise after the event"