1. to say that something someone else has said is wrong or not true
2. to be opposite to or inconsistent with something

Examples

• Don't contradict your teacher in front of the class.
• The witness contradicted his earlier testimony.
• Her actions contradict her words about caring for the environment.
• The new evidence contradicts the original theory.
• He always contradicts everything I say.
• The two reports contradict each other on several key points.