1. A white or gray marsupial and nocturnal animal (Didelphis virginiana) with a long nose, a long prehensile tail, a thick coat of hair, and lives in the eastern United States: "Susan was completely shocked when she suddenly came across an opossum while taking out the garbage in the evening. It seemed to be dead, but it was really just pretending!"
2. Etymology: from Algonquian opassum, opussum, or aposoum; the same as Proto-Algonquian "white" + "dog".