It's opposed to Windsor, also Harrow (4)
I believe the answer is:
eton
'harrow' is the definition.
(I've seen this in another clue)
'it's opposed to windsor' is the wordplay.
I cannot really see how this works, but
'to' is found in the answer.
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
A single letter 'n' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'also' is the link.
Can you help me to learn more?
(Other definitions for eton that I've seen before include "Posh English school of note" , "British public school of note" , "Town on the Thames noted for its school" , "Famous college" , "Public school founded in 1440" .)