turtleback

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Something shaped like the back of a turtle, especially.
• noun Nautical An arched structure erected over the deck of a ship as protection from heavy seas.
• noun Archaeology A stone tool with a convex side.

from The Century Dictionary.

• noun In mech.: A name given to rounded formations suggesting the carapace of the tortoise or turtle.
• noun A rounded-back cover of any structure, as over the rear of a motorcar whose frame is designed for the rear seats of the tonneau construction, but in which only two front seats are installed.
• noun See the extract.
• noun A West Indian helmet-shell, Cassis tuberosa.
• noun Something having the shape of a turtle's back.
• noun An arched protection erected over the upper deck of a steamer at the bow, and often at the stern also, to guard against damage from the breaking on board of heavy seas; a whaleback.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Archæol.) A rude stone celt of a form suggesting the back of a turtle.
• noun (Naut.) A convex deck at the bow or stern of a vessel, so made to shed the seas quickly.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Anything having the shape of a turtle's back (that is, its shell.)
• noun A library binding of a mass market paperback with a generic hardcover.
• noun A common name for plants of the genus Psathyrotes of annual and perennial forbs and low subshrubs native to dry areas of southwestern North America.