Y is for Yggdrasil
In Norse mythology/cosmology, Yggdrasil is the name of the vast tree around which earth, heaven, hell and all other worlds are arrayed. It is generally considered to be an ash tree, with branches and roots extending into all known realms.
The word is usually said to mean "Odin's Horse", deriving from Yggr, meaning Odin and drasill, a horse.
Archaeopteryx Blunderbuss Chthonic Dreadnought Entropy Fulgurite Gargantua Humbucking Ichthyic Juggernaut Kappa Labyrinthine Megrim Numinous Ophidian Pandemonium Quark Ragnarök Shibboleth Thing Umami Verdigris Worm Xanadu Yggdrasil