A matter or mouthful of moonshine; a trifle, nothing. The white brandy smuggled on the coasts of Kent and Sussex, and the gin in the north of Yorkshire, are also called moonshine.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Moon Rakers * MopNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes