Important stuff (8)
I believe the answer is:
material
I believe this clue is a double definition.
'important' is the first definition.
(material can mean significant)
'stuff' is the second definition.
(synonyms)
(Other definitions for material that I've seen before include "I am alert to find cloth or information" , "Tangible substance" , "Important; fabric" , "Matter; fabric" , "Fabric, stuff" .)