Window fitting, large, wedged in awkward position (5)
I believe the answer is:
blind
'window fitting' is the definition.
'large wedged in awkward position' is the wordplay.
'large' becomes 'l'.
'wedged in' is an insertion indicator.
'awkward position' becomes 'bind'.
'l' going into 'bind' is 'BLIND'.
(Other definitions for blind that I've seen before include "Unaware of" , "Like a bat" , "Sightless" , "shade" , "closed at one end" .)