Picture officer, one bound to retreat (6)
I believe the answer is:
fresco
'picture' is the definition.
(I know that fresco is a type of picture)
'officer one bound to retreat' is the wordplay.
'officer' becomes 'oc' (I've seen this in other clues).
'one bound' becomes 'serf' (someone bound to serve in feudal system).
'to retreat' shows that the letters should be reversed in order.
'oc'+'serf'='ocserf'
'ocserf' back-to-front is 'FRESCO'.
(Other definitions for fresco that I've seen before include "Forces (anag) - wall painting" , "Painting using watercolours on plaster" , "Artistic work" , "Work of art" , "Mural painting" .)