Definition of "jupon"

Some wore coat armour, imitating scale,And next their skins were stubborn shirts of mail;Some wore a breastplate and a light juppon,Their horses clothed with rich caparison;

1700, John Dryden, Palamon and Arcite‎, Book III

He climbed three marble steps, crossed the terrace and entered a dim foyer, where a chamberlain silently helped him from his helmet, his jupon and his chain cuirass.

1983, Jack Vance, chapter 26, in Lyonesse