KING ARTHUR, A game used at sea, when near the line, or in a hot latitude. It is performed thus: A man who is to represent king Arthur, ridiculously dressed, having a large wig made out of oakum, or some old swabs, is seated on the side, or over a large vessel of water. Every person in his turn is to be ceremoniously introduced to him, and to pour a bucket of water over him, crying, hail, king Arthur! if during this ceremony the person introduced laughs or smiles (to which his majesty endeavours to excite him, by all sorts of ridiculous gesticulations), he changes place with, and then becomes, king Arthur, till relieved by some brother tar, who has as little command over his muscles as himself.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Arsy varsey * ArticlesNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes