Eider are large seaducks in the genus Somateria, including:
- Common eider (Somateria mollissima)
- Spectacled eider (Somateria fischeri)
- King eider (Somateria spectabilis)
Eider may also refer to:
- Steller's eider (Polysticta stelleri) of the duck subfamily Merginae
- Eider (river), in Schleswig-Holstein, Germany
- Eider (Amt Kirchspielslandgemeinde), a collective municipality in Dithmarschen, Schleswig-Holstein, Germany
- Eider (brand), Korean company
- Surnames
- Max Eider (born Peter Millson), a guitarist and songwriter
- Rabbi Shimon Eider, a rabbi
- Forenames
- Eider Arévalo (born 1993), Colombian racewalker
- Eider Torres, (born 1983), baseball player from Venezuela
- Fictional characters
- Eider Duck, a Disney character who is Donald Duck's paternal uncle
- Sir Eider McDuck, a Disney character who is an ancestor of Scrooge McDuck and Donald Duck
- Aunt Eider, a Disney character who is the aunt of both Scrooge McDuck and John D. Rockerduck
- Ships
- USFS Eider, a motor schooner in commission in the U.S. Bureau of Fisheries from 1919 to 1940, U.S. Fish and Wildlife Service from 1940 to 1949, and U.S. Geological Survey from 1949 to 1954