leatherback Syllabification: (leath·er·back)Pronunciation: /ˈleT͟Hərˌbak/ (also leatherback turtle)Definition of leatherback noun a very large black turtle with a thick leathery shell, living chiefly in tropical seas. Dermochelys coriacea, the only member of the family Dermochelyidae leatherback in other Oxford dictionaries Definition of leatherback in the British & World English dictionary