Yggdrasil

Yggdrasil (from Old Norse Yggdrasill) is an immense mythical ash tree that plays a central role in Norse cosmology, where it is believed to exist in the center of cosmos as a connection between the Nine Worlds of Norse mythology. It is also called the World Tree, and by some the Tree of Life. There exists different intepretations of Norse cosmology and how Yggdrasil ties into it. The two most popular models is one where the worlds are located at different places along the trunk of the tree, at the end of the branches and at the roots, and one where the different worlds are placed around it in concentric circles. The Valhalla comics utilize a version of the latter model, with the tree growing at the center of Asgard, the realm of the Asir gods.

Etymology
The generally accepted meaning of Old Norse Yggdrasill is "Odin's horse", meaning "gallows". This intepretation comes about drasill means "horse" and Ygg(r)is one of Odin's many names. The Poetic Edda poem Hávamál describes how Odin sacrificed himself by hanging from a tree, making this tree "Odin's gallows". This tree may have been Yggdrasil. Gallows can be called "the horse of the hanged" and therefore Odin's gallows may have developed into the expression "Odin's horse", which then became the name of the great ash.

Nevertheless, scholars' opinions regarding the precise meaning of the name Yggdrasill vary, particularly on the issue of whether Yggdrasill is the name of the tree itself or if only the full term askr Yggdrasil (askr being Old Norse for "ash tree") refers specifically to the tree. According to this interpretation, askr Yggdrasils would mean the world tree upon which "the horse [Odin's horse] of the highest god [Odin] is bound." Both of these etymologies rely on a presumed by unattested *Yggdrasill.

F. Detter alternative offered the interpretation that the name Yggdrasill refers to the word yggr ("terror"), yet not in reference to the Odinic name, and so Yggdrasill would mean "tree of terror, gallows." F.R. Schröder has proposed that Yggdrasill may also mean "yew pillar", deriving yggia from *igwja (meaning "yew-tree"), and drasill from *dher- (meaning "support").

A third interpretation, presented by F. Detter, is that the name Yggdrasill refers to the word yggr ("terror"), yet not in reference to the Odinic name, and so Yggdrasill would then mean "tree of terror, gallows". F. R. Schröder has proposed a fourth etymology according to which yggdrasill means "yew pillar", deriving yggia from *igwja (meaning "yew-tree"), and drasill from *dher- (meaning "support").

Mythological background
Yggdrasil is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturlusson. In both sources, Yggdrasil is an immense ash tree that is the center of the cosmos and considered very holy. The gods go to Yggdrasil daily to assemble at their things, special traditional governing assemblies or councils. The branches of Yggdrasil extend far into the heavens, and the tree is supported by three roots that extend far into other locations; one to the well Urðarbrunnr (Urd's Welel) in the heavens, one of the spring Hvergelmir, and another to the well Mímisbrunnr (Mimir's Well). Creatures live within Yggdrasil, including the dragin Níðhöggr (Nidhogg), and the stags Dáinn, Dvalinn, Duneyrr and Duraþrór. There is also an eagle at the top of the tree, and the squirrel Ratatoskr who scurry up and down the tree's trunk carrying news and messages from the bottom of the tree to eagle at the top and vice versa.

Scholars generally consider Hoddmímis holt, Mímameiðr, and Læraðr to be other names for the tree. The tree is an example of sacred trees and groves in Germanic paganism and mythology, and scholars in the field of Germanic philology have long discussed its implications.