Definitions of clash:

• noun:   a state of conflict between persons
• noun:   a state of conflict between colors

  Example: "Her dress was a disturbing clash of colors"

• noun:   a minor short-term fight
• noun:   a loud resonant repeating noise
• verb:   be incompatible; be or come into conflict

  Example: "These colors clash"

• verb:   disagree violently

  Example: "We clashed over the new farm policies"

• verb:   crash together with violent impact

  Example: "Two meteors clashed"