Not completely comprehend every cry expressing derision (7)
I believe the answer is:
catcall
'derision' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'not completely comprehend every cry' is the wordplay.
I cannot really understand how this works, but
'completely' could be 'all' (synonyms) and 'all' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'expressing' is the link.
Can you help me to learn more?
(Other definitions for catcall that I've seen before include "Feline whistle of disapproval" , "Noisy expression of disapproval" , "Boo" , "Derisive cry" , "Audibly disapprove" .)