Zero movement in such a window (5)
I believe the answer is:
ogive
'such a window' is the definition.
(I have seen 'Gothic window' mean 'ogive' so perhaps 'window' could also mean 'ogive')
'zero movement' is the wordplay.
'zero' becomes 'O' (O resembles 0).
'movement' becomes 'give' (give can mean room to move).
'o'+'give'='OGIVE'
'in' acts as a link.
(Other definitions for ogive that I've seen before include "high-level support" , "Pointed or Gothic arch" , "Pointed arch; diagonal rib of vault (architecture)" , "pointed window" , "Gothic window" .)