Definition of "tonneau"

From the tonneau of Bentley's car the sheriff and Garland removed the groceries and sick-room supplies, stowing them in the kyacks.

1920, Peter B. Kyne, “The Understanding Heart”, in Ch.XV (Usenet)

The first step was to install a tonneau cover.

1982 March, “How to improve your pickup′s mileage”, in Popular Mechanics, page 102

It was flood-tide along Fifth Avenue; motor, brougham, and victoria swept by on the glittering current; pretty women glanced out from limousine and tonneau; young men of his own type, silk-hatted, frock-coated, the crooks of their walking sticks tucked up under their left arms, passed on the Park side.

1907 August, Robert W[illiam] Chambers, “His Own People”, in The Younger Set, New York, N.Y.: D. Appleton & Company, page 6

The first step was to install a tonneau cover. Now most pickup tonneaus snap onto studs screwed into the bodywork. The snaps rust, the holes in the truck rust and the tonneau—because the snaps are spaced every foot or so along the edges—eventually rips around the snaps.

1982 March, “How to improve your pickup′s mileage”, in Popular Mechanics, page 102

Tonneaux were made of the same plasticised canvas material used for soft-tops.

2003, Bill Piggott, Original Triumph TR4/4A/5/6: The Restorer′s Guide, unnumbered page