Some might say it’s Adam or I, grammatically speaking (5,6)
I believe the answer is:
first person
'speaking' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for first person that I've seen before include "Adam" , "Rebecca's written in it" , "royal "we", say" , "I or we (grammar)" , "was a faller at the outset" .)