Type of window (5)
I believe the answer is:
oriel
'type of window' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for oriel that I've seen before include "Style of window" , "Large recess - type of window" , "polygonal recess" , "This window projects from upper storey" , "place to study at Oxford" .)