cocktail gownn. a women's elegant semi-formal gown suitable for wearing at a cocktail party; cf. cocktail dressn.
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1935 Times 25 Nov. 17/5 A dinner or cocktail gown.
1993 N.Y. Times Mag. 24 Oct. 119/2 In 1953, a pale neurasthenic youth from French Algeria won the coveted International Wool Secretariat contest for dress design with a cocktail gown. Yves Saint Laurent was just 17.