A benefit on the other hand (5)
I believe the answer is:
again
'on the other hand' is the definition.
(thesaurus)
'a benefit' is the wordplay.
'benefit' becomes 'gain' ('gain' can be a synonym of 'benefit'**).
'a'+'gain'='AGAIN'
(Other definitions for again that I've seen before include "return" , "Furthermore" , "Repeatedly" , "On the other hand" , "repeat order" .)