Cummerbund

 noun cum·​mer·​bund | \ ˈkə-mər-ˌbənd  , ˈkəm-bər- \variants: or less commonly cumberbund \ ˈkəm-​bər-​ˌbənd  \

: a broad waistband usually worn in place of a vest with men's dress clothes and adapted in various styles of women's clothes