1. determining or having the power to determine an outcome

- cast the decisive vote

- two factors had a decisive influence

Similar word(s): conclusive, crucial, important, deciding, determinant, determinative, determining, fatal, fateful, peremptory

2. unmistakable

- had a decisive lead in the polls

Similar word(s): definite

3. characterized by decision and firmness

- an able and decisive young woman

- we needed decisive leadership

- she gave him a decisive answer

Similar word(s): resolute, unhesitating, resolute

4. forming or having the nature of a turning point or crisis

Similar word(s): crucial, important, critical

Sentences with decisive as an adjective:

- A decisive battle is fatal for one side's war chances

- A noble instance of this attribute of the decisive character. -J. Foster.