This is the 874th most frequent Russian word.
важное
Important.
In this sentence, the word 'важное' acts as an attributive adjective agreeing in gender and case with the noun 'дело' (matter).
Это очень важное дело.
This is a very important matter.
Here 'важное' functions as a predicative noun derived from the adjective, emphasizing its significance independently.
Не упусти важное!
Don't miss the important thing!
In this statement, 'важное' is used as a substantive noun, signifying crucial aspects of life.