fancy dress

noun fancy dresses

1. Australia, UK, uncountable, usually A costume, disguise to masquerade as something or someone else. And yet here he was, if one could credit one's senses, about to take part in a fancy-dress ball, a form of entertainment notoriously a testing experience for the toughest. And he was attending that fancy-dress ball, mark you--not, like every other well-bred Englishman, as a Pierrot, but as Mephistop
2. uncountable, usually Formalwear.
3. uncountable, usually Used other than figuratively or idiomatically: see fancy, dress.