A tooth. A queer cog; a rotten tooth. How the cull flashes his queer cogs; how the fool shews his rotten teeth.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Cog * To CogNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes