Níðhöggr

65. There comes the dark dragon flying from beneath the glistening serpent, from Nida-fels. On his wings bears Nidhögg, flying o'er the plain, a corpse. Now she will descend.

Níðhöggr gnaws at the tree from beneath. Both Grímnismál and Gylfaginning mention it. The squirrel Ratatoskr carries messages between Níðhöggr and the eagle in the branches.

The second half of the name means hewer, so the whole suggests a biter or striker. The first half is uncertain: it may be niðr (down), giving something like Biter Below; or níð, a word for social disgrace, giving Malice Striker; or it may connect with Niðafjöll, perhaps meaning dark. That last root has no known cognates, and even the length of the first vowel is not fixed in the sources. In Völuspá the creature lies among the dead in a hall of serpents and, at the poem's end, arrives as a winged serpent from the Niðafjöll. Scholars mostly take that as a sign of Ragnarök; others read it as renewal, or as a sinking that refers to the seeress rather than the serpent.