1.nounThe rear body or compartment of some types of motor vehicle, especially one containing seats for passengers.
2.nounAn old-style open passenger vehicle with a tonneau (rear compartment with seats).
"He has spent ten years lovingly restoring a rather luxurious tonneau with teak panelling and leather seats."
3.nounA protective covering which may be secured over the exposed portion of a motor vehicle, such as the seating area of an open sports car or the back of a pickup truck.