1. a fictional radioactive mineral from the planet Krypton that weakens or harms Superman
Usage: from DC Comics; often capitalized in reference to the fictional substance
2. something that is a person's or thing's fatal weakness or source of vulnerability
Usage: informal; figurative use

Examples

• In the Superman comics, kryptonite is the only substance that can weaken the superhero.
• Public speaking is his kryptonite; he becomes nervous and forgets what to say.
• The team's kryptonite has always been their weak defense.
• She discovered that sugar was her kryptonite when trying to lose weight.
• The company's kryptonite is its inability to adapt to new technology.
• For many students, math is their academic kryptonite.