Also found in: Medical, Wikipedia.
Something that presents a particular threat to one that is otherwise powerful: Immigration reform turned out to be the senator's kryptonite.
[After Kryptonite, a fictional radioactive mineral (the presence of which weakens the superhero Superman) appearing in Superman comics from 1949 onwards : Krypton, the home planet of Superman where Kryptonite was once found before being scattered in the universe by the planet's destruction (named by American comics writer Jerry Siegel (1914-1996), perhaps after the element krypton) + -ite.]
informal something that renders a person or thing helpless: football movies are box-office kryptonite.
[C20: from the fictional substance to which the hero is vulnerable in the comic strip Superman]