Etymology From a fictional radioactive element, kryptonite, that has a detrimental effect on the otherwise invulnerable character Superman. Formed from Superman's home planet Krypton + -ite, which was named after the chemical element krypton.
1
Figuratively, Usually The one weakness of something or someone that is otherwise invulnerable.
The terrific seven-grain bread here is the kryptonite of restaurant reviewers: two mini-loaves and you are incapacitated.1991 October 25, Bryan Miller, “Restaurants: John Clancy's”, in The New York Times, archived from the original on 12 Feb 2021:
So while recording or sampling a Charlie Manson track […] makes for shock rock kudos aplenty, a devotion to Hubbard is kryptonite for credibility.2006 March 25, Jonathan Leggett, “Cult musicians”, in The Guardian, archived from the original on 26 Feb 2025:
2 more examples
We all have our own kryptonite or kryptonites, so don't tempt yourself by listening to so-called friends who are just demonic tools being used to bring you under.2016, Marlon Orlando Cole, Orphans: Nature's Beloved, page 93:
But of course porn is kryptonite to many investors.2025 May 24, “OnlyFans has a shot at ditching its NSFW image”, in FT Weekend (Lex. section), London: The Financial Times Ltd., →ISSN, →OCLC, page 20:
Etymology From a fictional radioactive element, kryptonite, that has a detrimental effect on the otherwise invulnerable character Superman. Formed from Superman's home planet Krypton + -ite, which was named after the chemical element krypton.
1
To expose to, or attack with, kryptonite.
And even those two were pretty puny, like Superman after he had been kryptonited.1998, Phillip Gwynne, Deadly Unna?, Melbourne: Penguin, page 173:
2
Figuratively To destroy, wreck, or ruin; to affect adversely, as Superman is affected by kryptonite.