tonneau

Ton­neau is a term of French origin meaning a small barrel or cask. In English usage, it has taken on several related meanings connected by the idea of a container or rear compartment.

In wine and storage terminology, tonneau refers to a large cask or barrel used for aging or transporting liquids such as wine, spirits, or oil. The word historically described containers large enough to hold significant quantities and was applied to various sizes of barrels in distilling and winemaking traditions.

In historical automotive and carriage contexts, tonneau described a rear seating area or a body style that included a separate passenger compartment behind the front seats. Early motor vehicles and carriages sometimes used the term to distinguish the rear passenger cabin from the driver's area, with descriptions such as two-tone or multi-occupant tonneau configurations appearing in period catalogs and designs. The usage reflects the term’s barrel-like sense of enclosing a space or volume.

In modern automotive usage, tonneau most commonly appears in two forms. The tonneau cover is a cover for a pickup truck’s cargo bed, protecting contents from weather and theft and available in various mechanisms such as vinyl roll-up, rigid retractable, or hinged designs. The term is also used to describe the cargo area itself in some contexts, and in some regions, a pickup bed may be colloquially referred to as the tonneau.

Outside of vehicles, tonneau remains a historical term for large barrels used in the storage and transport of liquids, and it appears in antique and collectible contexts related to cooperage and wine cask design.