Source : Webster's Revised Unabridged Dictionary (1913)

Emergency \E*mer"gen*cy\, n.; pl. {Emergencies}. [See
   {Emergence}.]
   1. Sudden or unexpected appearance; an unforeseen occurrence;
      a sudden occasion.

            Most our rarities have been found out by casual
            emergency.                            --Glanvill.

   2. An unforeseen occurrence or combination of circumstances
      which calls for immediate action or remedy; pressing
      necessity; exigency.

            To whom she might her doubts propose, On all
            emergencies that rose.                --Swift.

            A safe counselor in most difficult emergencies.
                                                  --Brougham.

   Syn: Crisis; conjuncture; exigency; pinch; strait; necessity.

Source : WordNet®

emergency
     n 1: a sudden unforeseen crisis (usually involving danger) that
          requires immediate action; "he never knew what to do in
          an emergency" [syn: {exigency}, {pinch}]
     2: a state in which martial law applies; "the governor declared
        a state of emergency"
     3: a brake operated by hand; usually operates by mechanical
        linkage [syn: {hand brake}, {emergency brake}, {parking
        brake}]