Waistcoat n. : A short, sleeveless coat or garment for men, worn under the coat, extending no lower than the hips, and covering the waist; a vest.

Waistcoat n. : A garment occasionally worn by women as a part of fashionable costume.

Example:
What should i wear with a navy Waistcoat?

Taxonomy
waistcoat, waistcoat pocket, popularity, dress, vest, fashion, jacket, trousers, coat, suit, free encyclopedia, single-breasted, bottom button, clothing, History, tiny waist, buttonhole, black tie.

Defination from the web:
waistcoat (pronounced /ˈwɛskət/ or /ˈweɪstkoʊt/) , sometimes called a vest or a vestee in Canada and the US, is a sleeveless upper-body garment ... A waistcoat has a full vertical opening in the front which fastens with buttons or snaps. ...