noun (n)

• a situation in which no progress can be made or no advancement is possible(noun.state)

  Example:
  Reached an impasse on the negotiations.
  

  Synonym:
  dead end, deadlock, stalemate, standstill
  

  source: wordnet30
• a street with only one way in or out(noun.artifact)

  Synonym:
  blind alley, cul de sac, dead-end street
  

  source: wordnet30
• An impassable road or way; a blind alley; cul-de-sac; fig., a position or predicament affording no escape.(noun)

  source: webster1913