the only species (Dermochelys coriacea) of a family (Dermochelyidae) of tropical sea turtles, covered with a tough, leathery upper shell: it is the largest living turtle, weighing up to c. 725 kg (c. 1,600 lb)
See leatherback in American Heritage Dictionary 4
noun
The largest living sea turtle (Dermochelys coriacea), found in tropical waters and having a tough, leathery carapace with seven longitudinal ridges.