Cuts off the port facilities (5)
I believe the answer is:
docks
'cuts off' is the definition.
'docks' can be an answer for 'cuts' (docking is a kind of cutting). I am not sure about the 'off' bit.
'port facilities' is the wordplay.
'port' becomes 'dock' (both can mean an area where ships are unloaded).
'facilities' becomes 's' (I can't justify this - if you can you should believe this answer much more).
'dock'+'s'='DOCKS'
'the' is the link.
Can you help me to learn more?
(Other definitions for docks that I've seen before include "Trims (tail); arrives in port" , "Removes tail" , "Harbour" , "Cuts short; port features" , "Cuts short, curtails" .)