Source : Webster's Revised Unabridged Dictionary (1913)

Fireball \Fire"ball`\, n.
   Ball, or globular, lightning.

Fireball \Fire"ball`\, n.
   (a) (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.
   (b) A luminous meteor, resembling a ball of fire passing
       rapidly through the air, and sometimes exploding.

Source : WordNet®

fireball
     n 1: an especially luminous meteor (sometimes exploding) [syn: {bolide}]
     2: a highly energetic and indefatigable person [syn: {powerhouse},
         {human dynamo}, {ball of fire}]
     3: a ball of fire (such as the sun or a ball-shaped discharge
        of lightning)
     4: the luminous center of a nuclear explosion