Keep rook (6)
I believe the answer is:
castle
I believe this clue is a double definition.
'keep' is the first definition.
(I've seen this before)
'rook' is the second definition.
(I know that rook can be written as castle)
(Other definitions for castle that I've seen before include "Chateau" , "Fort" , "Make chess move involving king and rook" , "Large building; rook" , "Large fortified building" .)