Tenebris is a great sword that is wielded by the fallen angel Lucifer. The name 'Tenebris' is latin for 'darkness' which fits Lucifer's title as the Prince of Darkness. Tenebris is the first weapon created by Lucifer himself, and was also used to battle his elder brother, Michael.
After Lucifer's fall, the sword fell afterwards, and is said to have plunged in the depths of Hell unto a rock of brimstone where it is unable to be picked up by any demon or even ones of high power and authority like the princes of Hell or Archdemons.
This is evidence of the fact that the sword itself acts as though it were alive and consious, and therefore, answers only to its one true master, Lucifer.
With Tenebris, Lucifer is able to channel his power through the blade itself, allowing him to perform wide ranged attacks and long ranged as well. The sword also gives off a specific colorful glow when it becomes imbued with Lucifer's power. Example being a bright gold when he accesses his Light abilities, and a shadowy black/smoke when he accesses his Darkness abilities.