Definition of kryptonite in English:

kryptonite

Pronunciation /ˈkriptəˌnīt/ /ˈkrɪptəˌnaɪt/

noun

  • 1(in the fictional word of the comic book, TV, and film character Superman) an alien mineral that has the property of depriving Superman of his powers.

    • ‘the evil Lex Luthor diminishes Superman's powers with kryptonite’
    1. 1.1Something that can seriously weaken or harm a particular person or thing.
      ‘flip-flopping on issues can be kryptonite to presidential candidates’
      • ‘such uncertainties are kryptonite for the bond market’

Origin

1940s from Krypton, the name of Superman's home planet (kryptonite is usually depicted as a green mineral that came to earth from Krypton, following its destruction).