From Longman Dictionary of Contemporary Englishdressing-upˌdressing-ˈup British English, dress-up American English noun [uncountable] DGOa children’s game in which they put on special clothes and pretend that they are someone else
Examples from the Corpus
dressing-up• This involved quite elaborate dressing-up, and the fun and laughter of those Boxing Day nights was a treasure indeed.• Instead she advocated a return to elegance ... dressing-up in the widest, and often wildest, sense.• Such dressing-up was, like glam rock before it, a boys' affair. 