| sea duck | (n) any of various large diving ducks found along the seacoast: eider; scoter; merganser |
| Sea duck | (Zool.) Any one of numerous species of ducks which frequent the seacoasts and feed mainly on fishes and mollusks. The scoters, eiders, old squaw, and ruddy duck are examples. They may be distinguished by the lobate hind toe. [ 1913 Webster ] |