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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.


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[1]:
      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.


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