decisive in WordNet English dictionary

1. forming or having the nature of a turning point or crisis
   "a critical point in the campaign"; "the critical test"
   critical  decisive 
   
2. determining or having the power to determine an outcome
   "cast the decisive vote"; "two factors had a decisive influence"
   decisive 
   
3. characterized by decision and firmness
   "an able and decisive young woman"; "we needed decisive leadership"; "she gave him a decisive answer"
   decisive 
   
4. unmistakable
   "had a decisive lead in the polls"
   decisive