Merriam-Webster Collegiate Dictionary - platy

 I. adjective  Date: 1533 resembling a plate; also consisting of plates or flaky layers — used chiefly of soil or mineral formations  II. noun  (plural ~ or ~s or platies)  Etymology: New Latin Platypoecilus, former genus name of the fish  Date: 1931 either of two tropical American freshwater live-bearers (Xiphophorus maculatus and X. variatus) that have a highly variable often brilliant color and are popular aquarium fishes — called also ~•fish