A woman’s great coat. Also, a sheepish bashful young fellow: an allusion to Joseph who fled from Potiphar’s wife. You are Josephus rex; you are jo-king, i. e. joking.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
See also the definition in Nathan Bailey's 1736 dictionary of canting and thieving slang.
Jorum * JoskinNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes