A ceremony performed on boys perambulating the bounds of the parish on Whit-monday, when they have their posteriors bumped against the stones marking the boundaries, in order to fix them in their memory.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Bumper * BunNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes