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.
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            The object is made to flash upon the eye of the
            mind.                                 --M. Arnold.
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            A thought flashed through me, which I clothed in
            act.                                  --Tennyson.
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   3. To burst forth like a sudden flame; to break out
      violently; to rush hastily.
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            Every hour
            He flashes into one gross crime or other. --Shak.
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   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:

Flashing \Flash"ing\, n.
   1. (Engineering) The creation of an artificial flood by the
      sudden letting in of a body of water; -- called also
      flushing.
      [1913 Webster]

   2. (Arch.) Pieces of metal, built into the joints of a wall,
      so as to lap over the edge of the gutters or to cover the
      edge of the roofing; also, similar pieces used to cover
      the valleys of roofs of slate, shingles, or the like. By
      extension, the metal covering of ridges and hips of roofs;
      also, in the United States, the protecting of angles and
      breaks in walls of frame houses with waterproof material,
      tarred paper, or the like. Cf. Filleting.
      [1913 Webster]

   3. (Glass Making)
      (a) The reheating of an article at the furnace aperture
          during manufacture to restore its plastic condition;
          esp., the reheating of a globe of crown glass to allow
          it to assume a flat shape as it is rotated.
      (b) A mode of covering transparent white glass with a film
          of colored glass. --Knight.
          [1913 Webster]

   Flashing point (Chem.), that degree of temperature at which
      a volatile oil gives off vapor in sufficient quantity to
      burn, or flash, on the approach of a flame, used as a test
      of the comparative safety of oils, esp. kerosene; a
      flashing point of 100[deg] F. is regarded as a fairly safe
      standard. The burning point of the oil is usually from ten
      to thirty degree above the flashing point of its vapor.
      Usually called flash point.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flashing
    n 1: a short vivid experience; "a flash of emotion swept over
         him"; "the flashings of pain were a warning" [syn: flash,
         flashing]
    2: sheet metal shaped and attached to a roof for strength and
       weatherproofing

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "flashing":
   ablaze, aflame, aflicker, bickering, blazing, blinking, brave,
   bravura, braw, brief, brisk, burning, chichi, cometary, dancing,
   daring, dashing, dressy, exhibitionistic, flaming, flaring, flashy,
   flaunting, fleet, flickering, flickery, flicky, fluttering,
   fluttery, frilly, frothy, fulgurant, fulgurating, gallant, gay,
   glittering, jaunty, jazzy, lambent, meteoric, playing, quick,
   quivering, quivery, rakish, short, short and sweet, short-term,
   short-termed, showy, snazzy, speedy, splashy, splurgy, sporty,
   stroboscopic, swift, wavering, wavery