Painting on three hinged panels (8)
I believe the answer is:
triptych
'painting on three hinged panels' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for triptych that I've seen before include "Altarpiece" , "panel" , "Three-panel artwork" , "Artistic work on three panels" , "Three-panelled picture" .)