Daemon Weapon
Daemon Weapons are gifts of the Chaos Gods, unearthed by particluarly choice champions of Chaos. The Daemons are imprisoned in the weapon, but have a very powerful, persuasive, and sometimes detrimental effect to their holder if the wielder cannot firmly establish his mastery over the weapon.
The most famous of these daemon weapons is the Daemon Sword Drach'nyen, carried by Abaddon the Despoiler and harboring the daemon Drach'nyen. All that is known about Drach'nyen is that it can "rend reality apart". Also, unlike other weapons that occasionally attempt to subvert their bearer, Drach'nyen is under Abaddon's complete control.
Another well-known Daemon Weapon is the Gorechild, a massive chainaxe carried by Kharn the Betrayer. While in game terms Gorechild is not technically a Daemon Weapon, it does behave like a Daemon Weapon in the books. Gorechild continually beckons for Kharn to slay and slay to satiate the thirst of the Khorne-daemon bound within. And Kharn, the masochistic pawn of Khorne that he is, continually obliges.