All the guests were well-dressed for the formal event.

dressed 是动词 dress 的过去分词形式，dress 的意思是"穿衣、打扮"。 well-dressed 是由副词 well（好地）和过去分词 dressed（穿着）组成的复合形容词，表示"穿着得体、衣着讲究的"。