Pronunciation: (di-sī'siv),[key] —adj. 1. having the power or quality of deciding; putting an end to controversy; crucial or most important: Your argument was the decisive one. 2. characterized by or displaying no or little hesitation; resolute; determined: The general was known for his decisive manner. 3. indisputable; definite: a decisive defeat. 4. unsurpassable; commanding: a decisive lead in the voting.