noun (n)

• a usually secretive or illicit sexual relationship(noun.state)

  Synonym:
  affair, affaire, amour, intimacy, involvement
  

  source: wordnet30
• a channel for communication between groups(noun.communication)

  Example:
  He provided a liaison with the guerrillas.
  

  Synonym:
  contact, inter-group communication, link
  

  source: wordnet30
• A union, or bond of union; an intimacy; especially, an illicit intimacy between a man and a woman.(noun)

  source: webster1913