1. a person or thing that flashes.
  2. a flashing light operated by a switching device that automatically turns it on and off alternately.
  3. a signal light on an automotive vehicle that can be made to flash, as to indicate the intention of making a turn or to call attention to a vehicle that has slowed or stopped in a hazardous place.Compare turn signal.
  4. the switching device that operates such a light.
  5. Slang. a person, especially a man, who exposes the genitals suddenly, and usually briefly, in public.


  1. a brief, sudden burst of bright light: a flash of lightning.
  2. a sudden, brief outburst or display of joy, wit, etc.
  3. a very brief moment; instant: I’ll be back in a flash.
  4. Informal. flashlight(def 1).
  5. superficial, meretricious, or vulgar showiness; ostentatious display.
  6. Also called news flash. Journalism. a brief dispatch sent by a wire service, usually transmitting preliminary news of an important story or development.Compare bulletin(def 2).
  7. Photography.
    1. bright artificial light thrown briefly upon a subject during an exposure.
    2. flash lamp.
    3. flashbulb.
    4. flashtube.
  8. the sudden flame or intense heat produced by a bomb or other explosive device.
  9. a sudden thought, insight, inspiration, or vision.
  10. Slang. rush1(def 26).
  11. Metallurgy.
    1. a ridge of metal left on a casting by a seam between parts of the mold.
    2. a ridge formed at the edge of a forging or weld where excess metal has been squeezed out.
  12. Poker. a hand containing all five suits in a game played with a five-suit pack.
  13. a device, as a lock or sluice, for confining and releasing water to send a boat down a shallow stream.
  14. the rush of water thus produced.
  15. hot flash.
  16. Obsolete. the cant or jargon of thieves, vagabonds, etc.

verb (used without object)

  1. to break forth into sudden flame or light, especially transiently or intermittently: a buoy flashing in the distance.
  2. to gleam.
  3. to burst suddenly into view or perception: The answer flashed into his mind.
  4. to move like a flash.
  5. to speak or behave with sudden anger, outrage, or the like (often followed by out): to flash out at a stupid remark.
  6. to break into sudden action.
  7. Slang. to open one’s clothes and expose the genitals suddenly, and usually briefly, in public.
  8. Slang. to experience the intense effects of a narcotic or stimulant drug.
  9. to dash or splash, as the sea or waves.
  10. Archaic. to make a flash or sudden display.

verb (used with object)

  1. to emit or send forth (fire or light) in sudden flashes.
  2. to cause to flash, as powder by ignition or a sword by waving.
  3. to send forth like a flash.
  4. to communicate instantaneously, as by radio or telegraph.
  5. to make an ostentatious display of: He’s forever flashing a large roll of bills.
  6. to display suddenly and briefly: She flashed her ID card at the guard.
  7. to change (water) instantly into steam by pouring or directing onto a hot surface.
  8. to increase the flow of water in (a river, channel, etc.).
  9. Glassmaking and Ceramics.
    1. to coat (plain glass or a glass or ceramic object) with a layer of colored, opalescent, or white glass.
    2. to apply (such a layer).
    3. to color or make (glass) opaque by reheating.
  10. Building Trades. to protect from leakage with flashing.
  11. Cards. to expose (a card) in the process of dealing.
  12. Archaic. to dash or splash (water).


  1. sudden and brief: a flash storm.
  2. showy or ostentatious.
  3. caused by or used as protection against flash: flash injuries; flash clothing.
  4. counterfeit or sham.
  5. belonging to or connected with thieves, vagabonds, etc., or their cant or jargon.
  6. of or relating to followers of boxing, racing, etc.
  1. flash in the pan,
    1. a brief, intense effort that produces no really significant result.
    2. a person who makes such an effort; one who enjoys short-lived success.
  2. flash on, Slang.
    1. to have a sudden thought, insight, or inspiration about.
    2. to have a sudden, vivid memory or mental picture of: I just flashed on that day we spent at the lake.
    3. to feel an instantaneous understanding and appreciation of.


  1. something that flashes, such as a direction indicator on a vehicle
  2. British slang a person who indecently exposes himself


  1. a sudden short blaze of intense light or flamea flash of sunlight
  2. a sudden occurrence or display, esp one suggestive of brilliancea flash of understanding
  3. a very brief space of timeover in a flash
  4. an ostentatious displaya flash of her diamonds
  5. Also called: newsflash a short news announcement concerning a new event
  6. Also called: patch mainly British an insignia or emblem worn on a uniform, vehicle, etc, to identify its military formation
  7. a patch of bright colour on a dark background, such as light marking on an animal
  8. a volatile mixture of inorganic salts used to produce a glaze on bricks or tiles
    1. a sudden rush of water down a river or watercourse
    2. a device, such as a sluice, for producing such a rush
  9. photog informal short for flashlight (def. 2), flash photography
  10. a ridge of thin metal or plastic formed on a moulded object by the extrusion of excess material between dies
  11. Yorkshire and Lancashire dialect a pond, esp one produced as a consequence of subsidence
  12. (modifier) involving, using, or produced by a flash of heat, light, etcflash blindness; flash distillation
  13. flash in the pan a project, person, etc, that enjoys only short-lived success, notoriety, etc


  1. informal ostentatious or vulgar
  2. informal of or relating to gamblers and followers of boxing and racing
  3. sham or counterfeit
  4. informal relating to or characteristic of the criminal underworld
  5. brief and rapidflash freezing


  1. to burst or cause to burst suddenly or intermittently into flame
  2. to emit or reflect or cause to emit or reflect light suddenly or intermittently
  3. (intr) to move very fasthe flashed by on his bicycle
  4. (intr) to come rapidly (into the mind or vision)
  5. (intr; foll by out or up) to appear like a sudden lighthis anger really flashes out at times
    1. to signal or communicate very fastto flash a message
    2. to signal by use of a light, such as car headlights
  6. (tr) informal to display ostentatiouslyto flash money around
  7. (tr) informal to show suddenly and briefly
  8. (intr) British slang to expose oneself indecently
  9. (tr) to cover (a roof) with flashing
  10. to send a sudden rush of water down (a river, etc), or to carry (a vessel) down by this method
  11. (in the making of glass) to coat (glass) with a thin layer of glass of a different colour
  12. (tr) to subject to a brief pulse of heat or radiation
  13. (tr) to change (a liquid) to a gas by causing it to hit a hot surface
  14. obsolete to splash or dash (water)

“male genital exhibitionist,” 1960s (though meat-flasher in this sense was attested in 1890s); agent noun from flash (v.).


1560s, from flash (v.); originally of lightning. Meaning “first news report” is from 1857. Meaning “photographic lamp” is from 1913. The comic book character dates to 1940. Flash in the pan (1809) is from old-style guns, where the powder might ignite in the pan but fail to spark the main charge.


late 14c., from flasken (c.1300) “to dash or splash” (as water), probably imitative. Related: Flashed; flashing. Sense of “give off a sudden burst of light or flame” is 1540s. Flash flood is from 1940. Flash card is from 1923. Flash cube (remember those?) is from 1965.

In addition to the idiom beginning with flash

  • flash in the pan

also see:

  • in a flash
  • quick as a wink (flash)
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