What is "river duck"

River \Riv"er\, n. [F. riv[`e]re a river, LL. riparia river, bank of a river, fr. L. riparius belonging to a bank or shore, fr. ripa a bank or shore; of uncertain origin. Cf. Arrive, Riparian.]

1. A large stream of water flowing in a bed or channel and emptying into the ocean, a sea, a lake, or another stream; a stream larger than a rivulet or brook.

   Transparent and sparkling rivers, from which it is delightful to drink as they flow.
   --Macaulay.

2. Fig.: A large stream; copious flow; abundance; as, rivers of blood; rivers of oil. River chub (Zo["o]l.), the hornyhead and allied species of fresh-water fishes. River crab (Zo["o]l.), any species of fresh-water crabs of the genus Thelphusa, as Thelphusa depressa of Southern Europe. River dragon, a crocodile; -- applied by Milton to the king of Egypt. River driver, a lumberman who drives or conducts logs down rivers. --Bartlett. River duck (Zo["o]l.), any species of duck belonging to Anas, Spatula, and allied genera, in which the hind toe is destitute of a membranous lobe, as in the mallard and pintail; -- opposed to sea duck. River god, a deity supposed to preside over a river as its tutelary divinity. River herring (Zo["o]l.), an alewife. River hog. (Zo["o]l.)

   1. Any species of African wild hogs of the genus Potamoch[oe]rus. They frequent wet places along the rivers.

   2. The capybara.

      River horse (Zo["o]l.), the hippopotamus.

      River jack (Zo["o]l.), an African puff adder ( Clotho nasicornis) having a spine on the nose.

      River limpet (Zo["o]l.), a fresh-water, air-breathing mollusk of the genus Ancylus, having a limpet-shaped shell.

      River pirate (Zo["o]l.), the pike.

      River snail (Zo["o]l.), any species of fresh-water gastropods of Paludina, Melontho, and allied genera. See Pond snail, under Pond.

      River tortoise (Zo["o]l.), any one of numerous fresh-water tortoises inhabiting rivers, especially those of the genus Trionyx and allied genera. See Trionyx.