Decisive
decisive /dɪˈsaɪsɪv/
adj. 果断的，决定性的，坚定的
It means that someone is able to decide sth. quickly and with confidence; or refers to a particular situation which is very important for the final result.
它指的是某人能迅速且自信地决定某事;或指某种对最终结果非常重要的特定情况。
Our team needs a more decisive team leader.
我们的队伍需要一位更加果断的队长。
We all know that she has played a decisive role in the negotiations.
众所周知，她在谈判中起到了关键作用。
