A conventional sort of farewell for the PM? (4,9)
I believe the answer is:
good afternoon
'the pm?' is the definition.
The answer and definition 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?
'a conventional sort of farewell' is the wordplay.
'a conventional sort of' becomes 'good' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'farewell' becomes 'afternoon' (afternoon is a kind of farewell).
'good'+'afternoon'='GOOD AFTERNOON'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for good afternoon that I've seen before include "PM greeting" , "Words of salutation" .)