College style window (5)
I believe the answer is:
oriel
This clue is a triple definition!
'college' is the first definition.
(Oxford University college)
'style' is the second definition.
(I have seen 'Style of window ' mean 'oriel' so perhaps 'style' could also mean 'oriel')
'window' is the third definition.
(oriel is a type of window)
(Other definitions for oriel that I've seen before include "Upstairs bay window" , "Type of bay window" , "Recessed bay window" , "Loire (anag.)" , "English college" .)