To seize, or catch unawares. To nab the teaze; to be privately whipped. To nab the stoop; to stand in the pillory. To nab the rust; a jockey term for a horse that becomes restive. To nab the snow: to steal linen left out to bleach or dry. Cant.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
nab * to nab girderNathan Bailey's 1721 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes