Additional material at the end (8)
I believe the answer is:
addendum
'additional material at the end' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for addendum that I've seen before include "Textual matter added on" , "Additional item at the end of a book" , "Additional material at the back of a book" , "Extra item added to book or text" , "Additional material at the end" .)