形容詞 decisive:

1. determining or having the power to determine an outcome
2. unmistakable
3. characterized by decision and firmness
4. forming or having the nature of a turning point or crisis
   同義詞：critical

1. The report brought about a decisive change in the whole policy.
   這個報告使整個方針發(fā)生了決定性的變化。
2. The enemy was defeated in a decisive battle.
   敵人在一場決定性的戰(zhàn)斗中被擊敗。
3. Be decisive, tell them exactly what you think should be done.
   果斷些，確切地告訴他們你認為應該怎么做。
4. The injury to their key player could be a decisive factor in the game.
   他們主力隊員受傷可能是這場比賽勝負的決定性因素。

de.ci.sive

adj.（形容詞）
Having the power to decide; conclusive.
決定性的：有權決定的；結論性的
Characterized by decision and firmness; resolute.
決斷的：具有果斷堅決的特征的；堅定的
Beyond doubt; unmistakable:
明確的：毫無疑問的；無誤的：
例句：
a decisive defeat.
確實無疑的失敗

【引伸】
deci.sively
adv.（副詞）
deci.siveness
n.（名詞）
<參考詞匯><同義詞>decisive,conclusive,crucial,definitive,determinativeThe central meaning shared by these adjectives is .determining or having the power to determine an outcome.:
這些形容詞共同的中心的含義是"決定性的，有權決定結果的"：
例句：
the decisive vote;
決定性的一票；

例句：
a conclusive reason;
決定性的理由；

例句：
crucial experiments;
關鍵的實驗；

例句：
a definitive verdict;
明確的裁決；

例句：
the determinative battle. indecisive
決定性的戰(zhàn)役 indecisive