in Norse mythology, the world tree, a giant ash supporting the universe. One of its roots extended into Niflheim, the underworld; another into Jötunheim, land of the giants; and the third into Asgard, home of the gods. At its base were three wells: Urdarbrunnr (Well of Fate), from which the tree was watered by the Norns (the Fates); Hvergelmir (Roaring Kettle), in which dwelt Nidhogg, the monster that gnawed at the tree's roots; and Mímisbrunnr (Mimir's Well), source of wisdom, for the waters of which Odin sacrificed an eye. After Ragnarök (q.v.; Doomsday), the world tree, though badly shaken, was to be the source of new life.