underdressed
US /ˌʌn.dɚˈdrest/
UK /ˌʌn.dɚˈdrest/

1.
salah kostum, kurang formal
wearing clothes that are too informal for a particular occasion
:
•
I felt completely underdressed at the fancy restaurant.
Saya merasa benar-benar salah kostum di restoran mewah itu.
•
She was worried she would be underdressed for the gala.
Dia khawatir akan salah kostum untuk acara gala.