kryptonite
noun [ U ] uk/ˈkrɪp.tən.aɪt/ us/ˈkrɪp.tə.naɪt/
氪（一种虚构的化学元素，存在于有关超人的故事中，可使超人丧失超常能力）
in stories and films, a fictional (= invented) substance that can hurt the character Superman, who is extremely strong and not hurt by most things
致命打击;致命弱点
something that hurts or damages a person or thing that usually seems strong
A slowing economy is kryptonite for the U.S. dollar. 经济放缓可能对美元造成致命打击。
His personal kryptonite comes in the form of a romantic entanglement. 陷入桃色纠葛是他的个人弱点。