verb (v)

• become dark or darker(verb.change)

  Example:
  The sky darkened.
  

  Antonym:
  lighten, lighten up
  

  source: wordnet30
• tarnish or stain(verb.contact)

  Example:
  A scandal that darkened the family's good name.
  

  source: wordnet30
• make dark or darker(verb.change)

  Example:
  Darken a room.
  

  Antonym:
  brighten, lighten, lighten up
  

  source: wordnet30
• To make dark or black; to deprive of light; to obscure; as, a darkened room.(verb)

  source: webster1913
• To grow or darker.(verb)

  source: webster1913