Capital friend raises with zero returns (6)
I believe the answer is:
dublin
'capital' is the definition.
(Dublin is an example)
'friend raises with zero returns' is the wordplay.
'friend' becomes 'bud' (shortly for buddy).
'raises' says the letters should be written backwards.
'with' says to put letters next to each other.
'zero' becomes 'nil' (synonyms).
'returns' is a reversal indicator.
'bud' back-to-front is 'dub'.
'nil' reversed gives 'lin'.
'dub'+'lin'='DUBLIN'
(Other definitions for dublin that I've seen before include "Capital of Eire" , "European city" , "European capital" , "Ulysses city (Joyce)" , "Irish capital city" .)