Towards the core (5)

I believe the answer is:
inner
(Other definitions for inner that I've seen before include "Bull's penned in by this" , "just missing the gold" , "Private, not expressed" , "Situated inside" , "may not satisfy this man" .)
I believe the answer is:
inner
(Other definitions for inner that I've seen before include "Bull's penned in by this" , "just missing the gold" , "Private, not expressed" , "Situated inside" , "may not satisfy this man" .)