A profit, and not for the first time (5)
I believe the answer is:
again
'not for the first time' is the definition.
(another time)
'a profit' is the wordplay.
'profit' becomes 'gain' (synonyms).
'a'+'gain'='AGAIN'
'and' acts as a link.
(Other definitions for again that I've seen before include "One more time, encore" , "Moreover - a second time" , "return" , "Not for the first time" , "10 10 [AGAIN" .)