Yapock \Ya"pock\ (?; 277), n. [Probably from the river Oyapok, between French Guiana and Brazil.] (Zo["o]l.) A South American aquatic opossum ({Chironectes variegatus}) found in Guiana and Brazil. Its hind feet are webbed, and its fore feet do not have an opposable thumb for climbing. Called also {water opossum}. [Written also {yapack}.]