1. A set of clothes worn to a party, celebration, or festive event, typically more formal or elaborate than everyday clothing
She wore a beautiful costume de festa to the wedding reception.
Ela usava um lindo costume de festa na recepção do casamento.
2. A disguise or themed outfit worn to costume parties or masquerade events
Everyone came in a costume de festa to the Carnival party.
Todos vieram em costume de festa para a festa de Carnaval.