CRUCIAL adjective /ˈkruːʃ(ə)l/
1.something that is crucial is extremely important because it has a major effect on the result of something
crucial for: The money is crucial for the research.
crucial to: Resolving this issue is crucial to making peace work.
it is crucial (that): It is crucial that all students develop these basic skills.
British (very informal) extremely good.
You can hear crucial here (The Devil Wears Prada):