He who pays the reckoning, or answers for the rest of the company: as, Will you stand godfather, and we will take care of the brat; i.e. repay you another time. Jurymen are also called godfathers, because they name the crime the prisoner before them has been guilty of, whether felony, petit larceny, &c.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Gobbler * GogNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes