The fairy which offers Orpheus for food in the infernal regions a roasted ant, a flea's thigh, butterflies' brains, some sucking mites, a rainbow-tart, and other delicacies of like nature, to be washed down with dewdrops, beer made from seven barleycorns, and the supernaculum of earth-born topers. (King: Orpheus and Eurydice.)
To seize without warning. A contraction of apprehend. (Norwegian, nappe, to catch at, nap, snatch; Swedish, nappa.) Our nap (to filch or steal) is a variety of the same word.
The keeper or catch of a latch or bolt is called the nab.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894