One too shrewd to take sour grapes (3)
I believe the answer is:
Here is my best explanation:
'sour grapes' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
I don't understand the rest of the clue.
(Other definitions for fox that I've seen before include "Baffle; mammal", "Sly type", "Trick", "Cunning animal", "Animal; to cheat", "Vulpine creature", "earth-dweller", "one with brush", "Countryside carnivore" and "Nonplus".)