One who is easily tricked out of his property; a term used by gaolers, for prisoners who have money and bleed freely.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Midshipman’s Watch and Chain * Milk and WaterNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes