I repeat, it’s a win (5)
I believe the answer is:
again
'i repeat it's' is the definition.
I can't judge whether this definition defines the answer.
'a win' is the wordplay.
'win' becomes 'gain' ('gain' can be a synonym of 'win'**).
'a'+'gain'='AGAIN'
Can you help me to learn more?
(Other definitions for again that I've seen before include "Anew" , "Repeatedly" , "return" , "On the other hand" , "Predictably perhaps" .)