Stay fresh in castle tower (4)
I believe the answer is:
keep
I believe this is a double definition.
'stay fresh' is the first definition.
(synonyms)
'castle tower' is the second definition.
(I've seen this before)
'in' is the link.
(Other definitions for keep that I've seen before include "Retain; stronghold" , "Eg, beef" , "Main tower of a medieval castle" , "Retain or care for" , "Look after" .)