waistcoatEnglishOxford New American Dictionarywaistcoat /ˈweskət, , ˈwɛskət , ˈwās(t)ˌkōt, ˈweɪs(t)ˌkoʊt / ▸ noun British a vest, especially one worn by men over a shirt and under a jacket. ▪ historical a man's quilted long-sleeved garment worn under a doublet in the 16th and 17th centuries.