Final answer:
Beowulf does not take a sword with a specific name into the lake, but he uses a sword called Hrunting and a giant's magical sword found in the lair to fight Grendel's Mother.
Step-by-step explanation:
The name of the sword Beowulf took with him into the lake is not explicitly mentioned in the old English epic poem Beowulf. However, Beowulf did take a sword provided to him by Unferth, called Hrunting, which failed against Grendel's Mother, and he subsequently found a giant's sword in her lair which he used to defeat her. This sword, made by giants and magical in nature, ultimately melted away to its hilt after Beowulf used it to kill Grendel's Mother, owing to her toxic blood. In the context of the passages provided, there are references to various weapons and armor typical of medieval literature and legends like Charlemagne's 'Joyeuse', King Arthur's 'Excalibur', and the shield and sword imagery in the story of Ethelred.