kryptonite
Americannoun
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Usually Kryptonite a fictional radioactive substance that is the only thing capable of hurting or weakening the otherwise invulnerable superhero Superman.
Exposure to Kryptonite nullifies Superman's powers and immobilizes him with pain.
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Sometimes Kryptonite something that a person or thing cannot defend against or defeat; a nemesis or bête noire.
The team has not found a way to stop the triple option attack, which has been their kryptonite over the last several years.
Garlic oil is kryptonite for aphids.
Etymology
Origin of kryptonite
Coined in 1943 by writer and producer George Lowther (1913–1975); krypton ( def. ) + -ite 1 ( def. )
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Early in 2026, in fact, tech was the market’s kryptonite, with once-hot software companies largely to blame for the trouble.
From Barron's ● May 1, 2026
“So 6,475 strike behaves like kryptonite for the market; it can repel price from above and below,” Kizemchuck said.
From MarketWatch ● Mar. 28, 2026
If you’re mad at the Dodgers don’t stop there — might as well don a cape and be super mad because MLB has no kryptonite against them.
From Los Angeles Times ● Jan. 17, 2026
Regardless, the book is Hedda’s kryptonite: Her lifestyle—the only reason she got married to begin with—has been built on the presumption that George will get the university job.
From The Wall Street Journal ● Oct. 28, 2025
“You do know that the word fine is basically kryptonite to a therapist’s ears, right?”
From "Far from the Tree" by Robin Benway
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
