Bay window (5)
I believe the answer is:
oriel
'bay window' is the definition.
(oriel is a type of bay window)
This is all the clue.
(Other definitions for oriel that I've seen before include "place to study at Oxford" , "Window built out from upper floor" , "Overhanging recess (window)" , "Type of window; Oxford college" , "This window projects from upper storey" .)