More old paintings put up (5)
I believe the answer is:
extra
'more' is the definition.
(thesaurus)
'old paintings put up' is the wordplay.
'old' becomes 'ex'.
'paintings' becomes 'art' (I've seen this before).
'put up' shows that the letters should be reversed in order.
'art' written backwards gives 'tra'.
'ex'+'tra'='EXTRA'
(Other definitions for extra that I've seen before include "Not a hit certainly" , "additional supplies" , "to boot" , "23 player?" , "Bonus; supplement" .)