Defensive position (7)
I believe the answer is:
redoubt
'defensive position' is the definition.
(type of fort)
This is all the clue.
(Other definitions for redoubt that I've seen before include "Temporary or outward fortification" , "Tube rod used in small fortification" , "Fieldwork defending a pass" , "Military defence-work" , "Keep losing confidence in" .)