Underdressed (adjective)

1. Not dressed in a suitable or appropriate way.
2. Not dressed in a way that is appropriate for the occasion or weather.

Origin:

19th century: from under- + dressed.

Examples:

1. She felt underdressed in her casual clothes at the formal event.
2. The guests at the wedding were underdressed, some wearing jeans and t-shirts.
3. He was underdressed for the cold weather and soon became chilled.
4. The underdressed models were shivering on the runway in the cold winter air.
5. The underdressed soldiers were ill-prepared for the harsh winter conditions.