On the other hand, it is a profit (5)
I believe the answer is:
Here is my best explanation:
'on the other hand' is the definition.
(I've seen this before)
'a profit' is the subsidiary indication.
'profit' becomes 'gain' ('gain' can be a synonym of 'profit').
'it is' is the link.
(Other definitions for again that I've seen before include "Not for the first time", "Predictably perhaps", "Anew", "Furthermore", "for another time", "One more time, encore", "return", "Encore, one more time", "On the other hand" and "Once more; on the other hand".)