From Longman Dictionary of Contemporary Englishfancy dressˌfancy ˈdress noun [uncountable] British English DCclothes that you wear, especially to parties, that make you look like a famous person, a character from a story etc an invitation to a fancy-dress party
Examples from the Corpus
fancy dress• No, I am not going to a fancy dress party, but to work.• A masked fancy dress ball in Cannes, especially at the Villa Russe, was an event.• Every day the children worry about their Hallowe'en costumes for the school fancy dress parade.• However, hand on heart, even if you are a top dressage rider, can you really justify the fancy dress?• Did you hear about the man who went to the fancy dress party as a bone?• In their fancy dress, they ordered pizza before going by motorcade to the Tennessee ball.• Less serious runners also compete wearing fancy dress.• A mini ramp jam with fancy dress and the odd one foot tail grab ollie. 