lightning

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

• noun An abrupt, discontinuous natural electric discharge in the atmosphere.
• noun The visible flash of light accompanying such a discharge.
• noun Informal A sudden, usually improbable stroke of fortune.
• intransitive verb To discharge a flash of lightning.
• adjective Moving or occurring with remarkable speed or suddenness.

from The Century Dictionary.

• noun A becoming light or less heavy; an exhilaration of the spirits.
• noun A becoming light or bright; a flashing of light: in this sense usually lightening.
• noun A sudden illumination of the heavens caused by the discharge of atmospheric electricity from one cloud to another or from a cloud to the earth; a flash of light due to electricity in the atmosphere.

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

• verb rare Lightening.
• noun A discharge of atmospheric electricity, accompanied by a vivid flash of light, commonly from one cloud to another, sometimes from a cloud to the earth. The sound produced by the electricity in passing rapidly through the atmosphere constitutes thunder.
• noun rare The act of making bright, or the state of being made bright; enlightenment; brightening, as of the mental powers.
• noun a rare form of lightning sometimes seen as a globe of fire moving from the clouds to the earth.
• noun lightning in angular, zigzag, or forked flashes.
• noun more or less vivid and extensive flashes of electric light, without thunder, seen near the horizon, esp. at the close of a hot day.
• noun (Telegraphy) a device, at the place where a wire enters a building, for preventing injury by lightning to an operator or instrument. It consists of a short circuit to the ground interrupted by a thin nonconductor over which lightning jumps. Called also lightning discharger.
• noun (Zoöl.) a luminous beetle. See Firefly.
• noun a lightning rod.
• noun a quick, penetrating glance of a brilliant eye.
• noun a metallic rod set up on a building, or on the mast of a vessel, and connected with the earth or water below, for the purpose of protecting the building or vessel from lightning.
• noun a diffused glow of electric light flashing out from the clouds, and illumining their outlines. The appearance is sometimes due to the reflection of light from distant flashes of lightning by the nearer clouds.

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

• noun The flash of light caused by the discharge of atmospheric electrical charge.
• noun The discharge of atmospheric electrical charge itself.
• noun figuratively Anything that moves very fast.
• adjective Extremely fast or sudden.
• adjective Moving at the speed of lightning.
• verb impersonal To produce lightning.

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

• noun abrupt electric discharge from cloud to cloud or from cloud to earth accompanied by the emission of light
• noun the flash of light that accompanies an electric discharge in the atmosphere (or something resembling such a flash); can scintillate for a second or more