tonneau

Noun

ton=neau

CIDE DICTIONARY

tonneau, n. [F.].

In France, a light-wheeled vehicle with square or rounded body and rear entrance. [Webster 1913 Suppl.]
Orig., the after part of the body with entrance at the rear (as in vehicle in def. 1); now, one with sides closing in the seat or seats and entered by a door usually at the side, also, the entire body of an automobile having such an after part. [Webster 1913 Suppl.]
same as Tonne. [Webster 1913 Suppl.]

tonneau, n. the part of a motor car occupied by the back seats, esp. in an open car.

Idiom

tonneau cover a removable flexible cover for the passenger seats in an open car, boat, etc., when they are not in use.

Etymology

F, lit. cask, tun