Board and lodging in central tower (4)
I believe the answer is:
keep
This clue is a double definition.
'board and lodging' is the first definition.
(I've seen this before)
'central tower' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for keep that I've seen before include "Main tower of a medieval castle" , "Fort" , "Guard" , "Act as custodian of" , "Retain possession of" .)