Profit from a gin (4)
I believe the answer is:
gain
'profit' is the definition.
(I know that profit can be written as gain)
'from a gin' is the wordplay.
'from' indicates an anagram (from the letters).
'a'+'gin'='agin'
'agin' anagrammed gives 'GAIN'.
(Other definitions for gain that I've seen before include "Obtain; benefit" , "Obtain; earn" , "Earn, profit" , "Increase; secure" , "Pick up" .)