A justacorps or justaucorps is a garment worn in the latter 17th century and earlier 18th century. Of French origin, the justacorps was a knee-length coat, fitted to the waist and flared below, without a waist seam. It featured deep, turn-back cuffs and was worn over a long vest or waistcoat and breeches.
The justacorps was an aristocratic garment worn primarily by men, although some women [e.g., Margaret Cavendish, Lady Newcastle ] wore the justacorps with a matching petticoat as a riding habit. http://en.wikipedia.org/wiki/Justacorps