The Collaborative International Dictionary of English v.0.48:

Flash \Flash\, n.; pl. Flashes.
   1. A sudden burst of light; a flood of light instantaneously
      appearing and disappearing; a momentary blaze; as, a flash
      of lightning.
      [1913 Webster]

   2. A sudden and brilliant burst, as of wit or genius; a
      momentary brightness or show.
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            The flash and outbreak of a fiery mind. --Shak.
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            No striking sentiment, no flash of fancy. --Wirt.
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   3. The time during which a flash is visible; an instant; a
      very brief period; as, I'll be back in a flash.
      [1913 Webster +PJC]

            The Persians and Macedonians had it for a flash.
                                                  --Bacon.
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   4. A preparation of capsicum, burnt sugar, etc., for coloring
      and giving a fictitious strength to liquors.
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   5. A lamp for providing intense momentary light to take a
      photograph; as, to take a picture without a flash.

   Syn: flashbulb, photoflash, flash lamp, flashgun.
        [WordNet 1.5]

   6. Same as flashlight. [informal]
      [PJC]

   7. (Journalism) A short news item providing recently received
      and usually preliminary information about an event that is
      considered important enough to interrupt normal
      broadcasting or other news delivery services; also called
      a news flash or bulletin.
      [PJC]

   Flash light, or Flashing light, a kind of light shown by
      lighthouses, produced by the revolution of reflectors, so
      as to show a flash of light every few seconds, alternating
      with periods of dimness. --Knight.

   Flash in the pan, the flashing of the priming in the pan of
      a flintlock musket without discharging the piece; hence,
      sudden, spasmodic effort that accomplishes nothing.
      [1913 Webster]