What is "justacorps"

n. (context historical English) A knee-length coat worn by men in the 17th and 18th centuries.

A justacorps or justaucorps is a long, knee-length coat worn by men in the latter half of the 17th century, and throughout the 18th century. The garment is of French origin, and was introduced in England as a component of a three-piece ensemble, also consisting of breeches and a long vest or waistcoat. This ensemble served as the prototype of the modern-day three-piece suit. The fabric selection and styling of the justacorps varied throughout time periods, as fashions frequently altered.