canard (n.)

"absurd or fabricated story intended as an imposition," 1851, perhaps 1843, from French canard "a hoax," literally "a duck" (from Old French quanart, probably echoic of a duck's quack); said by Littré to be from the phrase vendre un canard à moitié "to half-sell a duck," thus, perhaps from some long-forgotten joke, "to cheat." But also compare quack (n.1).