unmistakable; "had a decisive lead in the polls"

a move which alters or makes certain the result of a game: a decisive move may make an advantageous position a winning one, a decisive error may lose the advantage, or the game. Examples are to be found in the handout on Planning, and Kotov's Think Like a GM.

Having the power or quality of deciding a question or controversy; putting an end to contest or controversy; final; conclusive.

determining or having the power to determine an outcome; "cast the decisive vote"; "two factors had a decisive influence"

forming or having the nature of a turning point or crisis; "a critical point in the campaign"; "the critical test"

Marked by promptness and decision.

characterized by decision and firmness; "an able an decisive young woman"; "we needed decisive leadership"; "she gave him a decisive answer"