Type of window when set in concrete (8)
I believe the answer is:
casement
'type of window' is the definition.
(I've seen this before)
'when set in concrete' is the wordplay.
'when' becomes 'as'.
'set in' is an insertion indicator.
'concrete' becomes 'cement' (cement is a kind of concrete).
'as' going within 'cement' is 'CASEMENT'.
(Other definitions for casement that I've seen before include "Window opening on a vertical hinge" , "Hinged window-sash" , "Roger's window?" , "Side-opening window" , "Vertically hinged window" .)