Misericordia

The 'Misericordia' (High Gothic: "blade of mercy") is a bladed melee weapon in the form of a long dagger or short sword that was carried by the Custodians of first the Legio Custodes and after the Horus Heresy, the Adeptus Custodes. The blade was symbolic, intended to represent that the Custodes were beneficiaries of the Magisterium Lex Ultima which placed them above the reach of all Imperial Law save for the commandments of the Emperor of Mankind Himself. The Misericordia was designed to deliver a single, mortal blow, and despite their symbolic nature, were sometimes used by individual Custodians to carry out a death sentence or offer the Emperor's Peace to a mortally wounded and suffering warrior.

The Misericordia originated during on Terra during the Age of Strife, when they became symbols of the authority of the executioner-judges in the service of the tyrannical techno-barbarian warlords of Old Earth who held the ultimate power of life and death over all of their subjects. After the end of the Unification Wars, the Emperor adopted the old practice, but only Imperial agents and judges in the service of the Emperor were now allowed to carry the Misericordia.