Add to the end, nine, in one bit in the body or maybe not! (8)
I believe the answer is:
appendix
'one bit in the body or maybe not' is the definition.
I can't judge whether this definition defines the answer.
'add to the end nine' is the wordplay.
'add to the end' becomes 'append' (I've seen this before).
'nine' becomes 'IX' (roman numeral).
'append'+'ix'='APPENDIX'
'in' is the link.
Can you help me to learn more?
(Other definitions for appendix that I've seen before include "Section at end of a book" , "sometimes removed?" , "Table of subsidiary matter - vestigial organ" , "often discarded in theatre" , "Addendum - vestigial pouch in human intestines" .)