noun (n)

• a sudden unforeseen crisis (usually involving danger) that requires immediate action(noun.event)

  Example:
  He never knew what to do in an emergency.
  

  Synonym:
  exigency, pinch
  

  source: wordnet30
• a state in which martial law applies(noun.state)

  Example:
  The governor declared a state of emergency.
  

  source: wordnet30
• a brake operated by hand; usually operates by mechanical linkage(noun.artifact)

  Synonym:
  emergency brake, hand brake, parking brake
  

  source: wordnet30
• Sudden or unexpected appearance; an unforeseen occurrence; a sudden occasion.(noun)

  source: webster1913