In Dover, terminal is open (5)
I believe the answer is:
overt
'open' is the definition.
('overt' is associated in meaning with 'open')
'in dover terminal is' is the wordplay.
'in' indicates the answer is hidden within the clue.
'OVERT' is hidden within 'dover terminal is'.
(Other definitions for overt that I've seen before include "Open to view" , "Open and candid" , "Open,up front" , "Openly displayed" , "____ is able to be seen" .)