Father, gentleman going round capital city (5)
I believe the answer is:
paris
'capital city' is the definition.
(capital of France)
'father gentleman going round' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'gentleman' becomes 'sir' (a man may be addressed as sir).
'going round' says the letters should be written backwards.
'sir' reversed gives 'ris'.
'pa'+'ris'='PARIS'
(Other definitions for paris that I've seen before include "captivated Helen" , "where plaster comes from?" , "Helen's abductor" , "City where one may see the Mona Lisa" , "Arc de Triomphe city" .)