Stronghold, fortification (7)
I believe the answer is:
bastion
I believe this is a double definition.
'stronghold' is the first definition.
(bastion is a kind of stronghold)
'fortification' is the second definition.
(I know that bastion is a type of fortification)
(Other definitions for bastion that I've seen before include "staunch supporter" , "Stronghold, fortification" , "Projecting part of a fortification" , "A projecting fortification to increase angle of fire" , "Strong defender" .)