lightning

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An abrupt, discontinuous natural electric discharge in the atmosphere.
2. n. The visible flash of light accompanying such a discharge.
3. n. Informal A sudden, usually improbable stroke of fortune.
4. v. To discharge a flash of lightning.
5. adj. Moving or occurring with remarkable speed or suddenness.

Century Dictionary and Cyclopedia

1. n. A becoming light or bright; a flashing of light: in this sense usually lightening.
2. n. 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. The lightning-flash may have a length of a mile or even more, and commonly takes an irregular direction (forked lightning), the path of the electrical discharge being that of the least resistance. In sheet-lightning no definite spark is seen, but a general illumination over a broad surface; it is commonly due to the reflection by the clouds of the discharge proper. This is called summer lightning or heat-lightning when the storm is at a great distance, so that only the broad flashes of light are seen, usually near the horizon, and unaccompanied by thunder. Sheet-lightning is also described as occurring when there is neither storm nor cloud; if such cases be authentic, it is probably due to a weak electrical discharge in the air at a considerable altitude. In globular lightning or globe-lightning, which is a rare phenomenon, the discharge takes a spherical form (fire-ball), sometimes apparently a foot or more in diameter, and lasts for a number of seconds, descending slowly to the earth, and often exploding with a loud report. The discharge of frictional electricity in the laboratory gives phenomena similar in kind to those of lightning, and the “brimstone odor” which sometimes accompanies the latter (due to the formation of ozone) is often observed.
3. n. A becoming light or less heavy; an exhilaration of the spirits.

Wiktionary

1. n. The flash of light caused by the discharge of atmospheric electrical charge.
2. n. The discharge of atmospheric electrical charge itself.
3. n. Anything that moves very fast.
4. adj. Extremely fast or sudden.
5. adj. Moving at the speed of lightning.
6. v. To produce lightning.

GNU Webster's 1913

1. n. 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.
2. n. The act of making bright, or the state of being made bright; enlightenment; brightening, as of the mental powers.
3. v. Lightening.

WordNet 3.0

1. n. abrupt electric discharge from cloud to cloud or from cloud to earth accompanied by the emission of light
2. n. 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