The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
also Yg·dra·silnoun Mythology
The great ash tree that holds together earth, heaven, and hell by its roots and branches in Norse mythology.
Origin: Old Norse.