Thunder, the Elemental Sound

Thunder is revered sound tied to the element of lightning. Like the roar of fire, the surge of ocean water, the creak of wood, the tintinnabulation of ice, the clink of metal, the whistle of air, or the rumble of earth, thunder is considered an aspect of its parent element, Lightning.
Thunder is also name of an ancient magical relic from the eastern realms that would be eventually called Tzai-Léi, though it well predates such petty things as human nations and states. Thunder, the magic dagger, was said to be forged from primal thunder made solid and given form. As it is invested of great and ancient magics, and its tie to the elements, it can fly in air, cleave through wood and flesh, ripple with lightning, and disturb latent elemental forces around it. Thus, it is sought by power-seekers, and factions that would prevent it from falling into their hands.