flasher

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

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

Wiktionary

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

GNU Webster's 1913

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

WordNet 3.0

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