Hold the fort (4)
I believe the answer is:
keep
This clue is a double definition.
'hold' is the first definition.
(I know that hold can be written as keep)
'the fort?' is the second definition.
(I've seen this before)
(Other definitions for keep that I've seen before include "Board and lodging" , "Retain in old castle tower?" , "Main tower of a medieval castle" , "Conserve" , "Subsistence" .)