A waistcoat is a gentleman's garment from the Victorian Era. It is much like the men's vests of today.
Cut a sports coat so that it'll sit 1 inch above your waist line. Next, get a tailor to stich it back up. This might not work so be prepared to face any dificulties.
un gilet
Black legging with lace trim and thy-high boots.
He was wearing a waistcoat at the party.