|Origin:||From the sound of sharp blows|
if two armies, groups etc clash, they start fighting - used in news reports:
Troops clashed near the border.
Police have clashed with demonstrators again today.
if two people or groups clash, they argue because they have very different beliefs and opinions - used in news reports
Democrats clashed with Republicans in a heated debate.
The two men have clashed over the report's conclusions.
if two colours or designs clash, they look very bad together
I can't wear red - it clashes with my hair.
4 [intransitive] especially British English
if two events clash, they happen at the same time in a way that is inconvenient [= conflict American English]
The announcement has been delayed to avoid clashing with the Prime Minister's speech.
5 [intransitive and transitive]
if two pieces of metal clash, or if you clash them, they make a loud ringing sound:
The cymbals clashed.