Fr: coat. English: mantua.
Generic term for the coat-like, open-fronted female garment worn from the late 17th century until the French Revolution.
The manteau developed in the late 17th century with a full back and front pleated to fit the body. The pleats were held in place by a belt, sometimes also by hidden tacking, and the trained skirt gathered back and fixed with buttons or loops just above the derrière to form the characteristic "waterfall" folds. Hip pads were worn as skirt support, later - c1710 - also the very first, cone-shaped paniers.
The front of the bodice was first closed (c1685), later worn wide open (c 1690) to reveal a richly embroidered stomacher. From the short sleeves protruded those of the chemise, decorated with lace.
In France, it vanished after the death of Louis XIV (1715) and the subsequent turn towards looser gowns - most notably the contouche - but in England it survived in altered shape and was worn as often as the contouche.
Read more about the English mantua and its reappearance in France under robe á l'anglaise (it was AFAIK not refetred to as manteau then).
Examples of French manteaux:
very early 1680s manteau