矛盾
máo dùn
contradiction; conflict
noun
Example
他的话前后矛盾，让人很难理解他的真实想法。
Tā de huà qián hòu máo dùn, ràng rén hěn nán lǐjiě tā de zhēnshí xiǎngfǎ.
His words contradict each other, making it difficult to understand his true thoughts.
This word comes from an ancient Chinese story about a merchant who claimed to sell both an unstoppable spear (矛) and an impenetrable shield (盾). When asked what would happen if his spear struck his shield, he couldn't answer - hence the meaning of contradiction.