from
The Collaborative International Dictionary of English v.0.48
Tonneau \Ton`neau"\, n.; pl. {Tonneaux}. [F.]
1. In France, a light-wheeled vehicle with square or rounded
body and rear entrance.
[Webster 1913 Suppl.]
2. (Automobiles) 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.]
3. same as {Tonne}.
[Webster 1913 Suppl.]