A man who occupies two branches of one profession, is said to dragoon it; because, like the soldier of that denomination, he serves in a double capacity. Such is a physician who furnishes the medicines, and compounds his own prescriptions.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Draggletail * DrainNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes