Pronunciation: (kō-kē'nu),[key] —n. 1. Also called pompano, butterfly-shell clam. a small clam, Donax variabilis, abundant in the intertidal zone of eastern and southern U.S. coastal beaches, having fanlike bands of various hues, the paired empty shells often spread in a butterfly shape.
2. any similar clam, esp. of the genus Donax. 3. a soft, whitish rock made up of fragments of marine shells and coral, used as a building material.