costume UK /ˈkɒs.tjuːm/US /ˈkɑsˌt(j)um/noun 4verb 1forms 3 noun4 •A style of dress, including garments, accessories and hairstyle, especially as characteristic of a particular country, period or people.the sight of thousands of people gathered to watch men walk the streets openly in female costume — 1971 •special clothes that someone wears to pretend to be a different person or a creatureWe wore gorilla costumes to the party. •A set of clothes appropriate for a particular occasion or season.The bride wore a grey going-away costume. •A swimming costume.They call their bathing suits down there "costumes." — 1966 verb1 •To dress or adorn with a costume or appropriate garb. formscostumed · costuming · costumes