zug·un·ru·he or Zug·un·ru·he (tso?ok?o?on?ro?o-?)n. The migratory drive in animals, especially birds.[German : Zug, a pulling, move, migration; see zugzwang + Unruhe, restlessness (from Middle High German unruowe, from Old High German unruowa : un-, not; see ne in Indo-European roots + ruowa, rest).]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.