flasher

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A device that automatically switches an electric lamp off and on, as in a commercial display sign.
• noun Slang One who engages in indecent exposure; an exhibitionist.

from The Century Dictionary.

• noun Same as flusher.
• noun A device for automatically lighting and extinguishing incandescent lamps or groups of lamps: used especially in the operation of electric advertising-signs.
• noun One who or that which flashes.
• noun Specifically One who makes a show of more wit than he possesses.
• noun A hot boiler into which water is injected in small quantities and flashed into steam by the heat.
• noun A rower.
• noun In ichth, an acanthopterygian fish, the tripletail, Lobotes surinamensis, of the family Lobotidæ (which see); any lobotid.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who, or that which, flashes.
• noun A man of more appearance of wit than reality.
• noun A large sparoid fish of the Atlantic coast and all tropical seas (Lobotes Surinamensis).
• noun The European red-backed shrike (Lanius collurio); -- called also flusher.
• noun An exhibitionist{1}, especially a male, who briefly exposes his private parts in a public place.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Anything that flashes, especially a device that switches a light on and off.
• noun slang A person who exposes their genitals or female nipples.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an electrical device that automatically turns a lamp on and off (as for an advertising display)
• noun someone with a compulsive desire to expose the genitals
• noun a light that flashes on and off; used as a signal or to send messages