Longman Dictionary of Contemporary English
Wiktionary
n. Clothing of a particular style and colours worn to represent a country at international events, or as part of national celebrations.
Usage examples of "national costume".
They were dressed in the national costume of Lithuania, or Liechtenstein.
For the sake of convenience and comfort he resumed his national costume, thinking no harm.
There were Mexicans in big hats, and Africans in national costume, and the French incredibly chic in couture-designed clothes, and the English very formal, with the sexes sharply defined.
Your seductive friend, Karamaneh, is arrayed in her very becoming national costume in his honor, I presume.
Wooden plates hung on the wall : dancing couples in national costume.
The others endeavoured to persuade her to change her mind, and Gregory told her that even in a creation by Dior or Balmain, no Chinese woman looked so soigne and attractive as she did in her national costume.
The musical box underneath was still playing 'Wouldn't It Be Nice If Everyone Was Nice' but the rods that animated the figures had got twisted out of shape, so that the Klatchian boy was rhythmically hitting the Omnian girl over the head with his ceremonial spear, while the girl in Agatean national costume was kicking a small Llamedosian druid repeatedly in the ear.