A sleeveless, collarless garment worn over a shirt and under a suit jacket."waistcoat." Dictionary.com Unabridged (v 1.1). Random House, Inc. 09 Apr. 2007. ."waistcoat." Merriam-Webster Online. Merriam-Webster, Inc. 09 Apr. 2007.
A waistcoat is a sleeveless piece of clothing with buttons which people usually wear over a shirt. a piece of clothing without sleeves that has buttons down the front and is worn over a shirt, often under a jacket as part of a man's suit American Equivalent: vest