Ýdalir – Yew Dales or Yew Valley. The hall and/or realm of Ullr.
yfir – across, above
yfirmaðr – chieftain, leader
Yggdrasil – Óðin’s Horse, Óðin’s Gallows, or Yew Pillar. The World Tree which connects the Nine Worlds. Usually thought to be a giant ash tree.
Ýmir – the very first jötunn. He was born out of the rivers that formed in Ginnungagap. Óðin, Vili, and Vé killed him and turned his body into the various parts of the earth and sky.