fancy dress

fancy dress (usually uncountable, plural fancy dresses)

1. (UK, Australia) A costume, disguise to masquerade as something or someone else.
   • 1934, P. G. Wodehouse, Right Ho, Jeeves:

     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 Mephistopheles--this involving, as I need scarcely stress, not only scarlet tights but a pretty frightful false beard.

   • 2020 November 18, “Stop & Examine”, in Rail, page 71:

     Royal Mail worker Evette Chapman gathered a team of 12 colleagues to deliver post in fancy dress and raise money for a nurses' charity and patients in Musgrove Park Hospital, Taunton.

2. (uncountable) Formalwear.