Green’s Dictionary of Slang

a type of watch.

1876		C. Hindley Life and Adventures of a Cheap Jack 37: Mat [...] having on him a ‘duck,’ i.e., an old English watch movement in new silver cases. [Ibid.] 305: His trade had for years been selling ‘duck,’ i.e., metal-cased, watches.
1901		J. Caminada Twenty-Five Years of Detective Life II 107: It was a ‘duck’ (an old-fashioned worthless watch).