determining an outcome; or ending question; or describing something as unmistakable
She cast the decisive vote.
two factors had a decisive influence
had a decisive lead in the polls
she gave him a decisive answer
took decisive action against the Taliban
In the end, it is character that is the decisive factor in a person’s life.
Like many other crucially important technologies, hay emerged anonymously during the so-called Dark Ages. According to the Hay Theory of History, the invention of hay was the decisive event which moved the center of gravity of urban civilization from the Mediterranean basin to Northern and Western Europe. The Roman Empire did not need hay because in a Mediterranean climate the grass grows well enough in winter for animals to graze.
Freeman Dyson -- Infinite in All Directions
the decisive game seven of the series
The book is broken up into eight chapters, corresponding to eight years that had a decisive impact on our respective lives.