Much to everyone's astonishment, the underdog team won the championship.

astonishment 是名词，由动词 astonish（使惊讶）加上名词后缀 -ment 构成。astonish 本身来自古法语 estoner（震惊），与英语的 stun（使震惊）同源。astonishment 表示"惊讶、震惊"的状态或感受。