Lightning

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.

The act of making bright, or the state of being made bright; enlightenment; brightening, as of the mental powers.

Lightening.

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