noun (n)

• the act of intervening (as to mediate a dispute, etc.)(noun.act)

  Example:
  It occurs without human intervention.
  

  Synonym:
  intercession
  

  source: wordnet30
• a policy of intervening in the affairs of other countries(noun.communication)

  Synonym:
  interference
  Antonym:
  noninterference, nonintervention
  

  source: wordnet30
• the act or fact of interposing one thing between or among others(noun.act)

  Synonym:
  interposition
  

  source: wordnet30
• (law) a proceeding that permits a person to enter into a lawsuit already in progress; admission of person not an original party to the suit so that person can protect some right or interest that is allegedly affected by the proceedings(noun.act)

  Example:
  The purpose of intervention is to prevent unnecessary duplication of lawsuits.
  

  source: wordnet30
• care provided to improve a situation (especially medical procedures or applications that are intended to relieve illness or injury)(noun.act)

  Synonym:
  treatment
  

  source: wordnet30
• The act of intervening; interposition.(noun)

  source: webster1913