kryptonite

From a fictional radioactive element, kryptonite, that has a detrimental effect on the otherwise invulnerable character Superman. Apparently formed as krypton (“a chemical element, Kr”) +‎ -ite.

• IPA^(key): /ˈkɹɪptənaɪt/

kryptonite (uncountable)

1. (figuratively) The one weakness of something or someone that is otherwise invulnerable, an Achilles heel.
   • 1991 October 25, Bryan Miller, “Restaurants: John Clancy's”, in New York Times‎:

     The terrific seven-grain bread here is the kryptonite of restaurant reviewers: two mini-loaves and you are incapacitated.

   • 2006 March 25, Jonathan Leggett, “Cult musicians”, in The Guardian:

     So while recording or sampling a Charlie Manson track […] makes for shock rock kudos aplenty, a devotion to Hubbard is kryptonite for credibility.

• kryptonite on Wikipedia.Wikipedia