Green’s Dictionary of Slang

a type of crooked dice.

1552		G. Walker Detection of Vyle and Detestable Use of Dice Play 28: Light graviers there be, demies, contraries, and of all sorts, forged clean against the apparent vantage, which have special and sundry uses.
1591		Greene Notable Discovery of Coosnage in Grosart (1881–3) X 37: Pardon me Gentlemen for although no man could better then myself discouer this lawe and his tearmes, and the name of their Cheats, Barddice, Flats, Forgers, Langrets, Gourds, Demies, and many other, with their nature, & the crosses and contraries to them vpon aduantage, yet for some speciall reasons, herein I will be silent.
1608		Dekker Belman of London E3: The Names of false Dyce [...] A Bale of Demies.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1801		‘Modern Dict.’ in Sporting Mag. May XVIII .
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.