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
But Rybakina has emerged as the Belarusian's kryptonite after winning seven of their past nine hard court encounters.
From BBC ● Jan. 31, 2026
Plus, her ire and rage is kryptonite against those who’ve been “joined.”
From Los Angeles Times ● Dec. 24, 2025
But I remained strong, like miranium, ready to face her kryptonite.
From "Sir Fig Newton and the Science of Persistence" by Sonja Thomas
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.
