Definition of costume noun from the Oxford Advanced Learner's Dictionary

costume

noun
ˈkɒstjuːm
 
; ˈkɑːstuːm
 
 
1 [countable, uncountable] the clothes worn by people from a particular place or during a particular historical period see also national costume2 [countable, uncountable] the clothes worn by actors in a play or film/movie, or worn by somebody to make them look like something elseThe actors were still in costume and make-up.She has four costume changes during the play.He went to the party in a giant chicken costume.a costume designer3 [countable] (British English, informal) = swimming costumeIf you'd like a swim, we can lend you a costume.