A gin cocktail makes profit (4)
I believe the answer is:
gain
'profit' is the definition.
(I know that profit can be written as gain)
'a gin cocktail' is the wordplay.
'cocktail' indicates anagramming the letters.
'a'+'gin'='agin'
'agin' is an anagram of 'GAIN'.
'makes' acts as a link.
(Other definitions for gain that I've seen before include "Obtain; benefit" , "Benefit; put on (weight)" , "Obtain, secure" , "Advance" , "Obtain; earn" .)