My lovely ornamental moulding (7)
I believe the answer is:
cornice
'ornamental moulding' is the definition.
(I've seen this before)
'my lovely' is the wordplay.
'my' becomes 'cor' (both are expressions of surprise).
'lovely' becomes 'nice' (both can mean pleasant).
'cor'+'nice'='CORNICE'
(Other definitions for cornice that I've seen before include "Overhanging ledge of frozen snow" , "Ledge of snow overhanging a precipice" , "Ornamental wall moulding" , "decorative part of room" , "decorative feature" .)