Surprising thing not to say to a goose? (3)
I believe the answer is:
boo
'surprising thing' 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 can't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for boo that I've seen before include "Make one's dislike heard" , "Startling utterance" , "I don't like that!" , "Cry that shocks" , "Sound made to show disapproval or contempt" .)