Once more a profitable deal (5)
I believe the answer is:
again
'once more' is the definition.
(synonyms)
'a profitable deal' is the wordplay.
I cannot quite see how this works, but
'a' is within the answer.
'profitable' could be 'gain' (I've seen this in other clues) and 'gain' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for again that I've seen before include "Not for the first time" , "repeat order" , "return" , "Next time" , "Here we go ___" .)