decisive, crucial
Eh, ¡esto era nada menos que un progreso decisivo!
Wow, this was nothing short of a decisive breakthrough!
— Divorzio all'italiana (1961)
Allí iba a suceder el acontecimiento más decisivo de su vida.
There, the most decisive event of his life was about to take place.
This is the decisive duel.
Pensé que era el momento más decisivo de mi vida.
I thought it was the most decisive moment of my life.
— Despedidas (2008)