Green’s Dictionary of Slang

Derwent n.

(Aus.) a type of dice-pot that permits a skilled thrower to manipulate the dice as desired.

[Aus]Mirror (Sydney) 31 Aug. 8/2: A ‘Derwent’ has a little break or ridge around the lip of the pot which permits the expert thrower to cast the dice in such a way that he wins every time he wants to. It is said that the term arose in Tasmania, where the break was supposed to represent the river Derwent.

In compounds

Derwent Duck (n.)

(Aus.) an inhabitant of Tasmania.

[Aus]Chron. (Adelaide) 24 Mar. 43/3: [Nicknames for] Tasmanians, Van Diemenese, Derveners, Derwent Ducks, Mountain Devils, Tassies and Tassylanders.
Derwent pot (n.)

(Aus. Und.) a dice pot that has been prepared to permit illicit manipulation of the dice.

[Aus]Mirror (Sydney) 31 Aug. 8/2: Every confidence man ‘travels’ with all sorts of traps for the mugs. There is the ‘derwent’ pot, the ‘slithery,’ the top-sider, and the ‘rail-way.’ These are specially prepared pots, or dice boxes, which a skilful manipulator uses at his discretion.