Look after stronghold (4)
I believe the answer is:
keep
This clue is a double definition.
'look after' is the first definition.
(synonyms)
'stronghold' is the second definition.
(I know that keep is a type of stronghold)
(Other definitions for keep that I've seen before include "Board and lodging" , "Retain in old castle tower?" , "Guard" , "strong position" , "Conserve" .)