The Collaborative International Dictionary of English v.0.48:
eveningwear \eveningwear\ n. attire to wear on formal occasions in the evening. Syn: formalwear, evening dress, evening clothes. [WordNet 1.5]WordNet (r) 3.0 (2006):
eveningwear n 1: attire to wear on formal occasions in the evening [syn: formalwear, eveningwear, evening dress, evening clothes]