noun
decider; person who decides
Less common than the factor sense; used for a person or party whose judgment or action settles the matter, especially where someone has the deciding role.
賛否が同数なら、委員長が決め手になる。
If the votes are tied, the committee chair becomes the decider.
noun
decisive factor; clincher; key; trump card; conclusive evidence
The common modern use: the factor, evidence, move, or blow that settles a choice, argument, contest, or outcome. Often appears as 決め手になる, 決め手を欠く, or 決め手がない.
価格の安さが購入の決め手になった。
The low price was the deciding factor in the purchase.
犯人を特定する決め手がまだない。
There is still no conclusive evidence identifying the culprit.
終盤の三ポイントシュートが試合の決め手となった。
The three-point shot near the end became the decisive play of the game.
Often means a decisive blow, point, or piece of evidence; stronger and more punch-like than 決め手, which can be any key factor.
Means the authority or right to decide; useful when referring to decision-making power rather than the factor that settles the matter.
A distinct word especially used for the winning technique in sumo; 決め手 is broader and means a decisive factor or clincher.
A compound of 決め, the continuative noun-like form of 決める, and 手, which can mean a person involved in an action or a means/move. The spelling 決め手 is conventionally tied to deciding or settling something.