School near Windsor Castle (4)
I believe the answer is:
eton
'school near windsor castle' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for eton that I've seen before include "Leading English public school" , "Public school, established in 1440" , "Town opposite Windsor on the Thames" , "College in Berkshire" , "Berkshire public school" .)