To come into conflict or engage in a fight. The two rival gangs clashed in the alleyway last night.
To be in opposition or disagreement. Their personalities often clash, leading to frequent arguments.
To create a jarring or discordant effect, especially in terms of colors or sounds. The bright red curtains clashed with the orange walls.
(of events) To occur at the same time, especially so as to cause inconvenience or difficulty. Her wedding date clashes with the annual conference.