1. a person who makes an important decision or has the authority to decide something
2. something that determines the outcome of a situation or contest
Usage: often used in sports contexts

Examples

• The CEO is the ultimate decider on all major company policies.
• As team captain, she was often the decider in close games.
• The final exam will be the decider for students on the borderline.
• His vote was the decider in the close election.
• The penalty kick served as the decider in the championship match.
• The judge acted as the decider in the dispute between neighbors.