Window, for instance, held by putty? (8)
I believe the answer is:
casement
'window' is the definition.
(I know that casement is a type of window)
'for instance held by putty?' is the wordplay.
'for instance' becomes 'as'.
'held by' means one lot of letters goes inside another.
'putty?' becomes 'cement' (putty is a kind of cement).
'as' inserted within 'cement' is 'CASEMENT'.
(Other definitions for casement that I've seen before include "Hinged window-sash" , "Irish nationalist" , "Window opening on a vertical hinge" , "Hinged window sash" , "Roger's window?" .)