Nothing possibly said about a parting word (5)
I believe the answer is:
adios
'a parting word' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'nothing possibly said about' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'possibly' indicates an anagram.
'about' means one lot of letters goes inside another.
'said' with letters rearranged gives 'adis'.
'o' inserted inside 'adis' is 'ADIOS'.
Can you help me to learn more?
(Other definitions for adios that I've seen before include "Goodbye (Spanish)" , "Goodbye (20 across)" , "Goodbye to Spain" , "See you in Ibiza" , "Goodbye, senor" .)