Racecourse near Windsor (5)
I believe the answer is:
ascot
'racecourse near windsor' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ascot that I've seen before include "sporting event" , "Necktie with wide square ends" , "Type of necktie" , "Racecourse near Windsor" , "Racecourse, home to the Gold Cup since 1807" .)