Fire·ball n.
 1. Mil. A ball filled with powder or other combustibles, intended to be thrown among enemies, and to injure by explosion; also, to set fire to their works and light them up, so that movements may be seen.
 2. A rare phenomenon often associated with or caused by lightning, resembling a luminous ball of fire passing rapidly through the air or along solid objects, then disappearing, and sometimes exploding.  It seldom lasts more than a few seconds.  Also called ball lightning, globe lightning, globular lightning, or kugelblitz.

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