LIGHTNING, n. that is, lightening, the participle present of lighten.
1. A sudden discharge of electricity from a cloud to the earth, or from the earth to a cloud, or from one cloud to another, that is, from a body positively charged to one negatively charged, producing a vivid flash of light, and usually a loud report, called thunder. Sometimes lightning is a mere instantaneous flash of light without thunder, as heat-lightning, lightning seen by reflection, the flash being beyond the limits of our horizon.
2. from lighten, to diminish weight. Abatement alleviation mitigation.