1. To fight or disagree with someone or something. My house is always full of yelling because my kids clash with each other on everything.

2. To contradict or be in disagreement with something. The governor's new tax plan clashes with his campaign promises. Our idea got rejected because it clashed with the boss's vision for our department.

3. To look visually displeasing when paired or juxtaposed with something, usually as of colors. That eyeshadow totally clashes with her skin tone, unfortunately. We're all wearing pink, so you're definitely going to clash with us if you wear orange.