Definitions

1. noun

a fictional radioactive mineral from the planet Krypton, the presence of which is harmful or lethal to beings from that planet, especially Superman.

“The news that Kryptonite was found on Earth sent the city into chaos.”

2. noun

a metaphorical or symbolic weakness or vulnerability.

“Her fear of public speaking was her kryptonite.”

3. noun

a substance or element that is toxic or poisonous.

“The lab worker handled the kryptonite with caution.”