The definition of kryptonite is Superman's ultimate weakness, or anything that causes someone's ultimate weakness.
An example of kryptonite is the one food a person is seriously allergic to.
Something that presents a particular threat to one that is otherwise powerful: Immigration reform turned out to be the senator's kryptonite.
Origin of kryptoniteAfter 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 1
- The one weakness of something or someone that is otherwise invulnerable, an Achilles' heel.