Port finally passed across (5)
I believe the answer is:
dover
'port' is the definition.
(I've seen this before)
'finally passed across' is the wordplay.
'finally' suggests the final letters.
'across' becomes 'over' ('over' can be a synonym of 'across').
The final letter of 'passed' is 'd'.
'd'+'over'='DOVER'
(Other definitions for dover that I've seen before include "Kentish port" , "There'll be blue clouds over the white cliffs here" , "Sort of sole" , "White cliffs port" , "Channel port" .)