This subject has substance (6)
I believe the answer is:
matter
I believe this clue is a double definition.
'this subject' is the first definition.
(synonyms)
'substance' is the second definition.
(synonyms)
'has' is the link.
(Other definitions for matter that I've seen before include "Subject; be important" , "Affair; be important" , "No . . . . . . - it is unimportant" , "Substance - signify" , "Substance; topic" .)