crucial
adjective 
(of a decision or event in the future) extremely important 

This will be a crucial decision for the education services because it sets the standard for all future years.
Wilson's evidence proved crucial to the legal case.
It is crucial that the problem is tackled immediately.

(British slang) If you describe something as crucial, you mean that it is very good. 

I've bought some crucial new trainers.

crucially
adverb 
This case will be crucially (=extremely) important for other people who have suffered mental and physical damage from the drug.