The mottled horny shell of the hawksbill and several other species of turtle, used in adding veneers to or inlaying jewelry and other objects. Quite popular since ancient times, but now only harvested in countries that don't have laws about endangered species. Most things in a tortoiseshell pattern are now plastic.

Also the name of any of several types of nymphalid butterflies (genus Nymphalis) and another name for the color pattern of the domestic cat consisting of patches of black, orange, and white (more commonly called "calico" now).