A woman’s under-petticoat. It’s all Dicky with him; i.e. it’s all over with him.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Dick * Dicked in the nobNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes