dressed up

Wearing formal (dress) clothes. / Wearing a costume.

Japanese Meaning

フォーマルな服装をしている / 仮装をしている

The guests were dressed up for the wedding.

ゲストは結婚式のために正装していた。

Sense（1）

Wearing formal (dress) clothes.

Everyone was so nicely dressed up for the wedding, I couldn't resist taking a picture.

Sense（2）

Wearing a costume.

more dressed up

（ comparative ）

most dressed up

（ superlative ）