If a fact, action, or event is decisive, it makes certain a particular result.
his decisive victory in the presidential elections.
他在这次总统选举中的决定性胜利。
If someone is decisive, they have or show an ability to make quick decisions in a difficult or complicated situation.
He should give way to a younger, more decisive leader.
他应该让位于更年轻、更果断的领导者。