Gain nothing, being a drunkard (4)
I believe the answer is:
wino
'a drunkard' is the definition.
(I've seen this in another clue)
'gain nothing' is the wordplay.
'gain' becomes 'win' (synonyms).
'nothing' becomes 'O' (O resembles 0).
'win'+'o'='WINO'
'being' is the link.
(Other definitions for wino that I've seen before include "Alcoholic" , "Habitual drunk" , "Down-and-out drunkard" , "Street drunkard" , "terrible boozer?" .)