Count as substance (6)
I believe the answer is:
This clue is a double definition.
'count' is the first definition.
(I know that count is a action)
'substance' is the second definition.
'as' is the link.
(Other definitions for matter that I've seen before include "Be of significance" , "It has mass and occupies space" , "That which occupies space in the visible world" , "Concern" , "Physical substance" .)