An instrument used in housebreaking. This instrument has not been long in use. It will cut a round piece about five inches in diameter out of a shutter or door.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Round Sum * Round MouthNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes