waistcoat

US /ˈwes.kət/
UK /ˈwes.kət/
"waistcoat" picture
1.

a sleeveless upper-body garment worn over a shirt and often under a jacket, forming part of a man's suit

:
He wore a three-piece suit with a matching waistcoat.
The groom chose a silk waistcoat for his wedding day.