聚 - Ju4 - Assemble, Gathering

聚會 - Ju4 Hui4 - Assemble Meeting — Gathering

According to Jenny, you can’t say party? Is she sure? 聚會, which is a gathering or a get-together is the closest you can get. There’s also 晚會 - Wan3 Hui4 - Evening Meeting, but I guess that sounds too formal, according to her. Then there’s 聯歡會 - Lian2 Huan1 Hui4 - Connect Joyful Meeting which is an expression she’s never heard, so who knows what the connotation is. You can also say it phonetically as Pai4 Dui4 but that would be cheating.

UPDATE: I no longer consider 派對 - Pai4 Dui4 - Party cheating, after I found this site: Partyman & Sunshiny’s Sweet Party!