Back pass? (6,6)
I believe the answer is:
return ticket
'back pass?' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'back pass?' is the wordplay.
'back' becomes 'return' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'pass?' becomes 'ticket' (pass is a kind of ticket).
'return'+'ticket'='RETURN TICKET'
Can you help me to learn more?
(Other definitions for return ticket that I've seen before include "Permit for round trip" , "No single" , "Two-way journey pass" , "Homeward passage" , "homing device?" .)