Every Monday throughout the year, but most particularly the 25th of October, being the anniversary of Crispinus and Crispianus.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Crispin * Crispin’s LanceNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes