kryptonite /ˈkɹɪptənaɪt/noun 2verb 2forms 3 noun2 •(figurative) The one weakness of something or someone that is otherwise invulnerable.The terrific seven-grain bread here is the kryptonite of restaurant reviewers: two mini-loaves and you are incapacitated. — 1991 •(slang) Crack cocaine. verb2 •To expose to, or attack with, kryptonite.And even those two were pretty puny, like Superman after he had been kryptonited. — 1998 •(figurative) To destroy, wreck, or ruin; to affect adversely, as Superman is affected by kryptonite. formskryptonited · kryptoniting · kryptonites