Definition of clincher noun from the Oxford Advanced Learner's Dictionary

 

clincher

 noun
noun
BrE BrE//ˈklɪntʃə(r)//
 
; NAmE NAmE//ˈklɪntʃər//
 
[usually singular](informal)
 
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a fact, a remark or an event that settles an argument, a decision or a competition There was a lot of circumstantial evidence but they still needed a clincher, something cast iron that would carry a conviction. Sixsmith scored the clincher (= the winning goal) after 81 minutes.
See the Oxford Advanced American Dictionary entry: clincher