To be, or not to be, that is the answer (4)
I believe the answer is:
verb
'answer' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for verb that I've seen before include "'In grammar, it denotes action (4)'" , "love, for example" , "A word that conveys action" , "Word that denotes an action or a state" , "Maybe protest" .)