i.e. Davy. A general name for a Welchman, St. David being the tutelar saint of Wales. Taffy’s day; the first of March, St. David’s day.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Tackle * Tag-rag and BobtailNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes