Discharge perhaps to be of importance (6)
I believe the answer is:
matter
I believe this is a double definition.
'discharge perhaps' is the first definition.
(I know that discharge is a type of material)
'be of importance' is the second definition.
(to matter is to be important)
'to' acts as a link.
(Other definitions for matter that I've seen before include "It has mass and occupies space" , "Be of significance" , "Substance; be important" , "Substance; topic" , "Substance or material - not spirit" .)