Gold-filled fort (4)
I believe the answer is:
knox
'gold-filled fort' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for knox that I've seen before include "Scotttish churchman" , "John --, Scottish religious reformer" , "Fort . . . . holds the USA's gold bullion" , "preacher" , "Theologian" .)