From Longman Dictionary of Contemporary Englishdress up phrasal verb1 DCDLto wear special clothes for fun, or to put special clothes on someone as He went to the party dressed up as a Chicago gangster. in I keep a box of old clothes for the children to dress up in.dress somebody ↔ up We dressed him up as a gorilla.2 DCto wear clothes that are more formal than the ones you would usually wear It’s a small informal party – you don’t have to dress up.3 dress something ↔ upINTERESTING to make something more interesting or attractive It was the old offer dressed up as something new. → dress→ See Verb table
Examples from the Corpus
dress up• Most kids love dressing up.• One of the students dressed up as a rabbit and marched around campus carrying a sign.• I came in to find that my daughter had dressed herself up in my clothes.• They were dressed up in old sheets, pretending to be ghosts.dress in• People get dressed up in caps and gowns.• We thought anyone who dresses up in dresses we want to go and see.• At midday all the people from Amantani dress up in traditional costume and they go up to the two centres.• Now he's taken to dressing up in young people's clothes. 