evening dress

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Clothing worn for evening social events.
• noun An evening gown.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable An elegant dress worn by women, especially for social events in the evening, evening gown
• noun uncountable formal attire worn for evening social events.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun attire to wear on formal occasions in the evening