decisive

determining or having the power to determine an outcome

• “cast the decisive vote”
• “two factors had a decisive influence”

unmistakable

• “had a decisive lead in the polls”

characterized by decision and firmness

• “an able an decisive young woman”
• “we needed decisive leadership”
• “she gave him a decisive answer”

forming or having the nature of a turning point or crisis

• “a critical point in the campaign”
• “the critical test”