Daughter having extra port (5)
I believe the answer is:
dover
'port' is the definition.
(English port)
'daughter having extra' is the wordplay.
'daughter' becomes 'd' (genealogical abbreviation).
'having' means one lot of letters go next to another.
'extra' becomes 'over' (both can mean left over).
'd'+'over'='DOVER'
(Other definitions for dover that I've seen before include "fish" , "Channel port" , "There'll be blue clouds over the white cliffs here" , "Be aware of" , "UK shipping forecast area" .)