Free admission to harbour for one going overseas (8)
I believe the answer is:
passport
'free admission' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'harbour for one going overseas' is the wordplay.
'harbour' becomes 'port' (I've seen this before).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'one going overseas' becomes 'pass' (I can't justify this - if you can you should give a lot more credence to this answer).
'port' after 'pass' is 'PASSPORT'.
'to' is the link.
Can you help me to learn more?
(Other definitions for passport that I've seen before include "one admits" , "Official document required for foreign travel" , "Carte blanche" , "International identification document" , "Authorization to go abroad and return" .)