a.

1. 決定性的，決定的
   a decisive moment in his career

   他事業上的關鍵時刻

2. 確定的
   He gave a decisive answer.

   他給了明確的答覆。

3. 堅決的，果斷的
   A decisive person is needed to deal with the situation.

   應付這一局面需要一個堅決果斷的人。

adj.

1. settling an issue quickly and effectively:
   a decisive battle.
2. able to make decisions quickly.