We were all astounded by the news of her sudden resignation.

astounded 是动词 astound 的过去分词形式。astound 由前缀 a-（加强语气）和词根 stound（古英语表示"震惊"）组成，意思是"使震惊、使大吃一惊"。astounded 表示"感到震惊的"，常用来形容对意外消息或事件的强烈反应。