(transitive) To resolve (a contest, problem, dispute, etc.); to choose, determine, or settle. (intransitive) To make a judgment, especially after deliberation. (transitive) To cause someone to come to a decision.

Is Decisive a noun or verb?

The act of deciding.

Is the word decisive an adjective?

decisive adjective - Definition, pictures, pronunciation and usage notes | Oxford Advanced American Dictionary at OxfordLearnersDictionaries.com.