Screen behind altar (7)
I believe the answer is:
reredos
'screen behind altar' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for reredos that I've seen before include "Hanging in church" , "Ornamental screen behind a church altar" , "Painted screen behind an altar" , "Wall decoration behind altar" , "Back of fireplace" .)