Enterprize, pursuit, or attempt: to be sick of the lay. It also means a hazard or chance: he stands a queer lay; i.e. he is in danger. Cant.
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.
lawful blanket * laystallNathan Bailey's 1721 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes