noun (n)

• a street with only one way in or out(noun.artifact)

  Synonym:
  cul de sac, dead-end street, impasse
  

  source: wordnet30
• (figurative) a course of action that is unproductive and offers no hope of improvement(noun.act)

  Example:
  All the clues led the police into blind alleys.
  So far every road that we've been down has turned out to be a blind alley.
  

  source: wordnet30