or Eyder, a river of Denmark, having its source in a small lake 8 miles S. of Kiel, flowing generally westward, and falling into the German Ocean at Tönningen, after a course of 90 miles, for 70 of which it is navigable. It forms with the Kieler Canal a navigable connection between the North Sea and the Baltic.

EIDER DUCK. See index to Ornithology.