From Lexicanum

A Diresword is an Eldar Power Weapon with a potent spirit trapped within the blade itself. These spirits are Eldar spirits implanted with a Spirit Stone. When a blow is struck, the spirit will attempt to destroy the enemy's mind. This action is similar to the Imperial Force Weapon used by psykers.

The first Diresword was created by the Phoenix Lord Asurmen and can be used by Dire Avenger Exarchs.

Sources

• Warhammer 40,000: Wargear

See also

• Eldar Weaponry