noun Anything having the shape of a turtle's back (that is, its shell).
noun A convex deck at the bow or stern of a vessel, designed to shed seawater quickly.
noun An armor layout with an armored deck which slopes downwards towards the sides of the ship and connects to the lower edge of the main belt armor, designed to deflect shells striking the ship on trajectories close to horizontal.
noun A primitive stone celt of a form suggesting the back of a turtle.
noun A library binding of a mass market paperback with a generic hardcover.
(The addition of quotations indicative of this usage is being sought:)
noun Any plant of the genus Psathyrotes of annual and perennial forbs and low subshrubs native to dry areas of southwestern North America.