Extra bit of fish was unwrapped (4)
I believe the answer is:
coda
'extra bit' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'fish was unwrapped' is the wordplay.
'fish' becomes 'cod' (type of fish).
'unwrapped' says to take the centre (the letters which wrap the word are removed).
The centre of 'was' is 'a'.
'cod'+'a'='CODA'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for coda that I've seen before include "Conclusion of work" , "End of movement" , "Final part of mus. structure" , "Final section" , "Closing passage of musical piece" .)