Addict from southeast in ancient city (4)
I believe the answer is:
user
'addict' is the definition.
(drug user)
'southeast in ancient city' is the wordplay.
'southeast' becomes 'SE' (synonyms).
'in' indicates putting letters inside.
'ancient city' becomes 'ur' (ancient Sumerian city state).
'se' inserted within 'ur' is 'USER'.
'from' is the link.
(Other definitions for user that I've seen before include "Drug taker" , "one has to employ" , "One taking advantage" , "One who works an appliance" , "Ruse for employer" .)