From Longman Dictionary of Contemporary Englishcocktail dressˈcocktail ˌdress noun [countable] DCa formal dress for wearing to parties or other evening social events
Examples from the Corpus
cocktail dress• I have seen her before, in a cocktail dress at some one's party, or at an exhibition perhaps.• And no, a little black cocktail dress will not do.• Ruth shifted uncomfortably in her azure crêpe de Chine cocktail dress.• Smart casual wear is quite in order for dinner time, but bring one cocktail dress for the Captain's cocktail party. 