Everyone was astounded when the magician made the elephant disappear in front of their eyes.

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"震惊"）组成，意思是"使极度震惊"。astounded 表示"感到极度震惊的"。