kryptonite

American  

[krip-tuh-nahyt] / ˈkrɪp təˌnaɪt /

noun

1. 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.

2. 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.

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Etymology

Origin of kryptonite

Coined in 1943 by writer and producer George Lowther (1913–1975); krypton ( def. ) + -ite ¹ ( def. )

Example Sentences

“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

Flores’s persistence has puzzled even some of his industry peers, who say that California’s regulatory regime is kryptonite for oil-and-gas firms.

From The Wall Street Journal • Nov. 27, 2025

For Ohtani’s hitting, pitching has been his kryptonite this season.

From Los Angeles Times • Oct. 17, 2025

Fearfulness and intellectual laziness are kryptonite to the imagination.

From Salon • Oct. 15, 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