Substance or general idea (4)
I believe the answer is:
gist
This clue is a double definition.
'substance' is the first definition.
(I know that substance can be written as gist)
'general idea' is the second definition.
(I've seen this in another clue)
(Other definitions for gist that I've seen before include "Real point or substance" , "The essential point of something" , "The pitch on the matter" , "Significance" , "Drift" .)