Is it dealt with at the end of a medical textbook? (8)
I believe the answer is:
appendix
'textbook?' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe there's a link between them I don't understand?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for appendix that I've seen before include "Extra section" , "Reference" , "that may have to be removed" , "Section at end of a book" , "part of book" .)