The Collaborative International Dictionary of English v.0.48:

Flash \Flash\ (fl[a^]sh), v. i. [imp. & p. p. Flashed
   (fl[a^]sht); p. pr. & vb. n. Flashing.] [Cf. OE. flaskien,
   vlaskien to pour, sprinkle, dial. Sw. flasa to blaze, E.
   flush, flare.]
   1. To burst or break forth with a sudden and transient flood
      of flame and light; as, the lighting flashes vividly; the
      powder flashed.
      [1913 Webster]

   2. To break forth, as a sudden flood of light; to burst
      instantly and brightly on the sight; to show a momentary
      brilliancy; to come or pass like a flash.
      [1913 Webster]

            Names which have flashed and thundered as the watch
            words of unnumbered struggles.        --Talfourd.
      [1913 Webster]

            The object is made to flash upon the eye of the
            mind.                                 --M. Arnold.
      [1913 Webster]

            A thought flashed through me, which I clothed in
            act.                                  --Tennyson.
      [1913 Webster]

   3. To burst forth like a sudden flame; to break out
      violently; to rush hastily.
      [1913 Webster]

            Every hour
            He flashes into one gross crime or other. --Shak.
      [1913 Webster]

   flash in the pan, a failure or a poor performance,
      especially after a normal or auspicious start; also, a
      person whose initial performance appears augur success but
      who fails to achieve anything notable. From 4th pan, n.,
      sense 3 -- part of a flintlock. Occasionally, the powder
      in the pan of a flintlock would flash without conveying
      the fire to the charge, and the ball would fail to be
      discharged. Thus, a good or even spectacular beginning
      that eventually achieves little came to be called a flash
      in the pan.

   To flash in the pan, to fail of success, especially after a
      normal or auspicious start. [Colloq.] See under Flash, a
      burst of light. --Bartlett.
      [1913 Webster +PJC]

   Syn: Flash, Glitter, Gleam, Glisten, Glister.

   Usage: Flash differs from glitter and gleam, denoting a flood
          or wide extent of light. The latter words may express
          the issuing of light from a small object, or from a
          pencil of rays. Flash differs from other words, also,
          in denoting suddenness of appearance and
          disappearance. Flashing differs from exploding or
          disploding in not being accompanied with a loud
          report. To glisten, or glister, is to shine with a
          soft and fitful luster, as eyes suffused with tears,
          or flowers wet with dew.
          [1913 Webster]

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.
      [1913 Webster]

            The flash and outbreak of a fiery mind. --Shak.
      [1913 Webster]

            No striking sentiment, no flash of fancy. --Wirt.
      [1913 Webster]

   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.
      [1913 Webster]

   4. A preparation of capsicum, burnt sugar, etc., for coloring
      and giving a fictitious strength to liquors.
      [1913 Webster]

   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]

The Collaborative International Dictionary of English v.0.48:

Pan \Pan\, n. [OE. panne, AS. panne; cf. D. pan, G. pfanne, OHG.
   pfanna, Icel., Sw., LL., & Ir. panna, of uncertain origin;
   cf. L. patina, E. paten.]
   1. A shallow, open dish or vessel, usually of metal, employed
      for many domestic uses, as for setting milk for cream, for
      frying or baking food, etc.; also employed for various
      uses in manufacturing. "A bowl or a pan." --Chaucer.
      [1913 Webster]

   2. (Manuf.) A closed vessel for boiling or evaporating. See
      Vacuum pan, under Vacuum.
      [1913 Webster]

   3. The part of a flintlock which holds the priming.
      [1913 Webster]

   4. The skull, considered as a vessel containing the brain;
      the upper part of the head; the brainpan; the cranium.
      --Chaucer.
      [1913 Webster]

   5. (Carp.) A recess, or bed, for the leaf of a hinge.
      [1913 Webster]

   6. The hard stratum of earth that lies below the soil. See
      Hard pan, under Hard.
      [1913 Webster]

   7. A natural basin, containing salt or fresh water, or mud.
      [1913 Webster]

   Flash in the pan. See under Flash.

   To savor of the pan, to suggest the process of cooking or
      burning; in a theological sense, to be heretical.
      --Ridley. Southey.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flash in the pan
    n 1: someone who enjoys transient success but then fails