costume party

基本解释

A friend once invited me to a costume party. When I got there, I found that he had fooled me.
有一次一位朋友邀请我参加化妆舞会。我到了以后发现他愚弄了我。
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In my own town we have a big costume party every year at my favorite local pub, and every year more Chinese are getting involved.
每年在我寓居的城镇里，咱们每年都会在一家我常常光临的酒吧举行大型化装舞会，而加入人数也是逐年增添。
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Expensive, realistic masks — the kind that are the hit of the costume party — are increasingly being used out of season, and not always for laughs.
如今，昂贵逼真的化装舞会面具越来越多地在淡季被使用，也不单单是为了搞笑。

Everyone loves a costume party. ." And when it's the world's biggest comic book convention - some find it simply too hard to resist dressing up.

One employee who took time off for what he called a family illness was found in a time-stamped Facebook photo at a costume party, all decked out.
FORBES: Magazine Article
If it is a family gathering and you are part of the family, try to show up and be with the family, then duck out and be Santa, then get out of costume and return to the party with as minimum fuss as possible.
FORBES: What Are the Keys to Playing a Good Santa Claus at a Children's Christmas Party?
Mr. MEAD: Well, the thing is, you have to remember that I'm, you know, I'm the mummy that cooked the dinner, and I'm the one that planned the owl party, and I'm the one making the ice cream treats, so the costume's got to be on the simple side.
NPR: Author Shares Tricks And Treats For All

a party where people wear special clothes that make them look like a particular character, animal or object

A costume party or costume ball is a party at which the guests try to look like famous people or people from history, from stories, or from particular professions.