Source : Webster's Revised Unabridged Dictionary (1913)

Sheldrake \Shel"drake`\, n. [Sheld + drake.]
   1. (Zo["o]l.) Any one of several species of large Old World
      ducks of the genus {Tadorna} and allied genera, especially
      the European and Asiatic species. ({T. cornuta, or
      tadorna}), which somewhat resembles a goose in form and
      habit, but breeds in burrows.

   Note: It has the head and neck greenish black, the breast,
         sides, and forward part of the back brown, the
         shoulders and middle of belly black, the speculum
         green, and the bill and frontal bright red. Called also
         {shelduck}, {shellduck}, {sheldfowl}, {skeelduck},
         {bergander}, {burrow duck}, and {links goose}.

   Note: The Australian sheldrake ({Tadorna radja}) has the
         head, neck, breast, flanks, and wing coverts white, the
         upper part of the back and a band on the breast deep
         chestnut, and the back and tail black. The chestnut
         sheldrake of Australia ({Casarca tadornoides}) is
         varied with black and chestnut, and has a dark green
         head and neck. The ruddy sheldrake, or Braminy duck
         ({C. rutila}), and the white-winged sheldrake ({C.
         leucoptera}), are related Asiatic species.

   2. Any one of the American mergansers.

   Note: The name is also loosely applied to other ducks, as the
         canvasback, and the shoveler.

Source : WordNet®

sheldrake
     n 1: large crested fish-eating diving duck having a slender
          hooked bill with serrated edges [syn: {merganser}, {fish
          duck}, {sawbill}]
     2: Old World gooselike duck slightly larger than a mallard with
        variegated mostly black-and-white plumage and a red bill