Nonsense, say, Liberal brought up (5)
I believe the answer is:
bilge
'nonsense' is the definition.
(thesaurus)
'say liberal brought up' is the wordplay.
'say' becomes 'eg'.
'liberal' becomes 'lib'.
'brought up' says the letters should be written backwards (down clues only).
'eg'+'lib'='eglib'
'eglib' written backwards gives 'BILGE'.
(Other definitions for bilge that I've seen before include "Piffle - part of hull" , "bull" , "Rubbish - water in boat" , "(Water at) bottom of ship" , "Hogwash" .)