To tip the velvet; to put one’s tongue into a woman’s mouth. To be upon velvet; to have the best of a bet or match. To the little gentleman in velvet, i. e. the mole that threw up the hill that caused Crop (King William’s horse) to stumble; a toast frequently drank by the tories and catholics in Ireland.
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.
Vaulting School * Venerable MonosyllableNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes