Profit from a gin cocktail (4)
I believe the answer is:
gain
'profit' is the definition.
(synonyms)
'a gin cocktail' is the wordplay.
'cocktail' indicates an anagram.
'a'+'gin'='agin'
'agin' with letters rearranged gives 'GAIN'.
'from' is the link.
(Other definitions for gain that I've seen before include "Obtain; benefit" , "Win" , "Obtain to one's advantage" , "Obtain, secure" , "Pick up" .)