costume party AmE
costume ball
fancy dress party BrE
fancy-dress party BrE
fancy-dress ball BrE

It seemed to be a costume party she was flinging.

She made her first mask 12 years ago for a costume party.

We're having a big costume party with them in December.

You go to his office and it looks like a costume party, the way those people are dressed.

You act like you're ready to make this a costume party.

We met at a costume party a couple of years ago.

If this is the 1930's, he must be on his way to a costume party.

At the end of term, a traditional costume party is held.

Soon the boys are off to the costume party on their motorcycles.

The jackets looked like something a woman might really wear to more than a costume party.