Cold unfortunately trapping one in port (6)
I believe the answer is:
calais
'port' is the definition.
(I've seen this before)
'cold unfortunately trapping one' is the wordplay.
'cold' becomes 'c' (eg on taps).
'unfortunately' becomes 'alas' ('alas' is used to express regret).
'trapping' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'alas' enclosing 'i' is 'alais'.
'c'+'alais'='CALAIS'
'in' is the link.
(Other definitions for calais that I've seen before include "French port for ferry to England" , "Mary Tudor said it would be found "lying in my heart"" , "French port opposite Dover" , "Nearest French port to England" , "French Channel port" .)