Not for the first time, one takes the profit (5)
I believe the answer is:
again
'not for the first time' is the definition.
(another time)
'one takes the profit' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'takes' is a charade indicator (letters next to each other).
'the profit' becomes 'gain' ('gain' can be a synonym of 'profit').
'a'+'gain'='AGAIN'
(Other definitions for again that I've seen before include "Here we go ___" , "repeat order" , "One more time, encore" , "10 10 [AGAIN" , "Ocne more" .)