Male garment worn under the coat (justaucorps) from the late 17th century onwards.
At first, the gilet was knee-length (i.e. as long as the justaucorps) and had sleeves, but they vanished soon. Many of the buttons and buttonholes were purely decorative, never meant to be closed. The gilet became shorter over time, less and less buttons working. Later, the back of the gilet was made of sheer silk as opposed to the embroidered front fabric to make it less sticky against the waistcoat, and it was only about hip-length, the front edge angling out from the belly to the sides.
Early gilet, 1690s
Shorter gilet, 1760s
Late, short gilet, 1780s