To blab, or discover secrets. The cull is leaky, and cackles; the rogue tells all. Cant. See LEAKY.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
See also the definition in Nathan Bailey's 1721 dictionary of canting and thieving slang.
cacafeugo * cacklerNathan Bailey's 1721 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes