ˈkɛɹ.əˌpeɪs ˈkjuːtɪkəl ˌɛ.pɪ.ˈdɜː.mɪs ˌɛ.pə.ˈdɝ.məs ʃɛl hard outer covering or case of certain organisms such as arthropods and turtles the outer layer of the skin covering the exterior body surface of vertebrates the dead skin at the base of a fingernail or toenail