婚礼上，宾客们都盛装出席。

At the wedding, all the guests were attired in their finest outfits.

attired 是动词 attire 的过去分词形式，在句中表示被动状态。attire 来自古法语，意思是"穿着、打扮"，通常指正式或考究的着装。 attired in 表示"穿着...服装"，这里指宾客们都穿着最精美的服装出席婚礼。