Port, unopened, settled (4)
I believe the answer is:
over
'settled' is the definition.
(thesaurus)
'port unopened' is the wordplay.
'port' becomes 'dover' (I've seen this before).
'unopened' means to remove the first letter.
'dover' with its first letter taken off is 'OVER'.
(Other definitions for over that I've seen before include "Finished like cricket session" , "See 23" , "A bowler's round in cricket" , "Completely ended" , "Unit of test" .)