A little dirty attorney, ready to undertake any litigious or bad cause: it is derived from the French words petit vogue, of small credit, or little reputation.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Pettish * PharaohNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes