Many left port (5)
I believe the answer is:
dover
'port' is the definition.
(English port)
'many left' is the wordplay.
'many' becomes 'd' (Roman numeral for 500).
'left' becomes 'over' (I've seen this in other clues).
'd'+'over'='DOVER'
(Other definitions for dover that I've seen before include "Be aware of" , "Channel port" , "fish" , "Cinque Port" , "Roved around the English port" .)