Excalibur

n. magic sword of King Arthur (in English Literature)

Excalibur or Caliburn is the mythical sword of King Arthur, sometimes attributed with magical powers or associated with the rightful sovereignty of Great Britain. Sometimes Excalibur and the Sword in the Stone (the proof of Arthur's lineage) are said to be the same weapon, but in most versions they are considered separate. The sword was associated with the Arthurian legend very early. In Welsh, the sword is called Caledfwlch.
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Noun
1. the legendary sword of King Arthur
(hypernym) sword, blade, brand, steel

(n.)
The name of King Arthur's mythical sword.
  

King Arthur’s sword , also known in Geoffrey of Monmouth as Caliburn. There is no historical evidence for or against such a sword, and the role of the blade varies wildly in the romances . In the most common appearances, the Lady of the Lake gives the sword to Arthur, though in modern renditions the sword is often taken from the stone, a twist on the blade of Balin of the Two Swords, which Merlin placed into the stone, eventually drawn by Galahad (Malory). Before dying, Arthur instructed Bedevere to throw the blade back into the lake, when a hand caught it and took it beneath the waves. In the Vulgate Cycle , Arthur requires this service of Girflet, who twice tries to fool Arthur into believing that he has so dispensed the blade, but is caught both times, eventually following the command and throwing it as instructed. The sword was given to have various magical powers: healing, etc., as was the scabbard, which was to make Arthur impervious to mortal blows so long as he retained it in his possession.