A European capital divided by river port (8)
I believe the answer is:
aberdeen
'port' is the definition.
(I've seen this before)
'a european capital divided by river' is the wordplay.
'european capital' becomes 'bern' (capital of Switzerland).
'divided by' is an insertion indicator.
'river' becomes 'Dee' (River Dee).
'bern' enclosing 'dee' is 'berdeen'.
'a'+'berdeen'='ABERDEEN'
(Other definitions for aberdeen that I've seen before include "city in Europe" , "PM, resigned over Crimea" , "Scottish port" , "Scottish North Sea city" , "University city in north-east Scotland" .)