[opos.sum] n, pl opossums also opossum [Virginia Algonquian, lit., white animal] (1610) 1: any of a family (Didelphidae) of American marsupials that usu. have a pointed snout and prehensile tail; esp: a common omnivorous largely nocturnal and arboreal mammal (Didelphis virginiana) of No. America having grayish to blackish fur with white on the cheeks
2: any of several Australian phalangers