tonneau

noun, plural ton·neaus, ton·neaux [tuh-nohz] /tʌˈnoʊz/.

1. a rear part or compartment of an automobile body, containing seats for passengers.
2. a complete automobile body having such a rear part.
3. a waterproof cover, generally of canvas or vinyl, that can be fastened over the cockpit of a roadster or convertible to protect the interior.

noun plural -neaus or -neaux (-nəʊ, -nəʊz)

1. Also called: tonneau cover
   1. a detachable cover to protect the rear part of an open car when it is not carrying passengers
   2. a similar cover that fits over all the passenger seats, but not the driver’s, in an open vehicle
2. rare the part of an open car in which the rear passengers sit