/ dɪˈsaɪsɪv; NAmE / adjective
1.
very important for the final result of a particular situation :
a decisive factor / victory / battle
She has played a decisive role in the peace negotiations.
a decisive step (= an important action that will change a situation) towards a cleaner environment
➡ note at essential
2.
able to decide sth quickly and with confidence :
decisive management
The government must take decisive action on gun control.
OPP indecisive
► de·cisive·ly adverb
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WORD ORIGIN
early 17th cent.: from French décisif , -ive , from medieval Latin decisivus , from decis- determined, from the verb decidere determine, from de- off + caedere cut.