Additional former paintings returned (5)
I believe the answer is:
extra
'additional' is the definition.
(I've seen this before)
'former paintings returned' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'paintings' becomes 'art' (painting is a type of artwork).
'returned' says the letters should be written backwards.
'art' in reverse letter order is 'tra'.
'ex'+'tra'='EXTRA'
(Other definitions for extra that I've seen before include "An increased amount" , "not included" , "Bit actor in film" , "Especially" , "Additional, more than expected" .)