Very: an epithet which in the English vulgar language is made to agree with every quality or thing; as, devilish bad, devilish good; devilish sick, devilish well; devilish sweet, devilish sour; devilish hot, devilish cold, &c. &c.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Devil’s Guts * Deusea VilleNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes